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1 Jim Binkley Border Gateway Protocol - An Introduction Network Routing class
2 Jim Binkley outline u overview/theory –history/topologies/2 kinds of BGP/basic idea as DV protocol/important ideas u protocol u database, IBGP issues, policy tricks, Cisco config minimal intro u problems including flapping/security
3 Jim Binkley bibliography u rfc 1771, "A Border Gateway Protocol 4", Yakov Rekhter, and Tony Li, 1995 u rfcs 1772-1774 related, other BGP rfcs exist u Books: –Moy's OSPF has a very good overview chapter –"Internet Routing Architectures", Halabi, Cisco Press, title should be "Fun with BGP" »entire book about BGP basically –IP Routing Protocols - U. Black, has a chapter –Huitema of course and Perlman, 2nd edition for a little contrarian thinking
4 Jim Binkley more RFCs (which can be state of the art in this case) u 1657 - BGP MIB (SMIv2) - 1994 u 2385 - Protection of BGP Sessions Via the TCP/MD5 Signature Option, Heffernan, 1998 u 2595 - Use of BGP-4 Multi-protocol Extensions for IPv6 Inter-Domain Routing u 2858 - Multi-protocol Extensions for BGP-4, Bates, et. al, June 2000 u route reflection/confederation/communities/ flapping as well + probably something else u rfc 3221 - recent experience (growth of table/s)
5 Jim Binkley history u GGP - gateway to gateway (you knew that?) - DV IGP used in ARPANET –had 2 out of 4 echo to learn if peer existed –explicit ACK of update u EGP - an EGP!, NSFNET time period –net had to be strictly hierarchical, no loops –metric-less since there could not be 2 paths u IDRP - "i drip, you drip, we all drip", OSI BGP equivalent, had influence on BGP u and one more... (next slide)
6 Jim Binkley history, cont u IDPR - Martha Steenstrup, RFC 1479 –LS EGP, competition for awhile with BGP »again with IPv6, deja vu all over again –not hop by hop, but source route –initial router determines path to other side –can thus enforce arbitrary policies »go to X, then Y, then turn left, you are at Grandma's –call this "flow setup" :-> ? –considering MPLS, there may be some irony here
7 Jim Binkley BGP history u some EGP problems drove BGP design –needed to tolerate multiple paths and choose –early policy experiments aided evolution u BGP-4 as BGP-3 did not speak CIDR u multi-protocol BGP recently introduced –can deliver IPv6 info –can deliver multicast group info and perform RPF function for "uber" PIM/SM
8 Jim Binkley basic idea "use TCP" u we use TCP between BGP peers, call the peers speakers (2 peers), port 179 –BGP is vc oriented, pt./pt. pair-wise, unicast u TCP handles many of the error problems, hence BGP can be simpler –and stream data –don't need our own reliable protocol, etc –can be multi-hop if that makes sense
9 Jim Binkley two kinds of BGP u External BGP, EBGP - exterior BGP connection between two separate AS –typically have direct link connection –over a T1, T3, OC-xyzzy, Ethernet segment –since two AS/two admins collide, this may take »lawyers, and contracts, and money u Internal BGP, IBGP - internal to AS –may be multi-hop –may need to send BGP updates across the AS
10 Jim Binkley how do we get reachability? u external BGP - usually same link –manually configured on some telco links –if same ethernet segment, ARP will do it for us u internal BGP - may be multi-hop –if so, rely on IGP to get the job done »note: BGP control and routed packets (data) –of course, that could include static routing –IGP/EGP convergence problem - touch on this later
11 Jim Binkley topologies u transit network - packets are routed thru it, may not source/sink –multiple external and internal BGP peers –likely to have full Inet routing table (>=75k) u multi-homed stub –stub does not have transit packets, src/sink only –> one way out - may be for redundancy –needs AS number u single stub - one way out only –doesn't need AS or BGP for that matter
12 Jim Binkley topo picture single stub/no BGP/no AS number multi-homed stub AS 1, uses BGP AS 2, transit inet Inet AS 3, transit
13 Jim Binkley stub routing (no need for BGP) u 1. simply use static route u 2. get default route dynamically using IGP, RIP, OSPF, whatever from ISP/transit u 3. use BGP (training-wheel version) –likely to have fake AS, private AS numbers exist, and ISP/transit system can simply not advertise them, instead make stub appear as part of its AS routing space
14 Jim Binkley BGP as routing protocol u Distance-Vector with a twist u basic BGP logical update consists of: –(ip network(D), subnet mask, "attributes") –this is oversimplified, deal with this later in protocol u we make routing decisions based on attributes (multiple) + manual configuration, however u one attribute is the Vector; i.e., the AS path expressed as a complete source route of AS u (to net 220.127.116.11, via AS 1,2,3,4,5)
15 Jim Binkley BGP AS path AS 1 AS 2 AS 3 AS 4 AS 5 AS 6 AS 7 AS 8 assume Net number and AS number the same assume multi- home stub link X
16 Jim Binkley A7 - BGP routing database for A1 then: u 1. to N1, via AS5, AS3, AS1, next hop IP, etc. (3 AS hops) u 2. to N1, via AS5, AS2, AS1, etc u 3. to N1, via AS4, AS5, AS3, AS1, etc u 4. to N1, via AS4, AS5, AS2, AS1, etc. u default policy may be to choose least hop count, therefore choose #1 above u what happens if link X goes away? u we can choose route #3, thru AS4, 4 hops
17 Jim Binkley route UPDATES u note that as route is forwarded, one's own AS is prepended u e.g., AS3 update about AS1 to AS5 –input AS1, output AS3, AS1 u this gives us a metric and it helps us remain loop- free at layer 3 –and handle loops at layer 2 u simple rule: if you see yourself in the AS path, that's a loop, (and an error)
18 Jim Binkley BGP is not RIP u does not send entire routing table every N seconds –sends full routing table at boot (good thing about TCP) –only sends updates upon change (new or withdrawals) u does not do count to infinity –stores multiple paths in database (RIB) and can choose new one if available –and know topology because of AS path (can't fool me) u routing updates may be chosen on best hop count in terms of # of AS, a default metric therefore exists (more on policy in a bit)
19 Jim Binkley e.g., back at AS path picture u if using RIP, AS2 might be told by AS1, AS3, is one hop, therefore AS2 might tell AS1, AS3 is two hops –but mean two hops thru A1 ?! u with BGP, AS1 sends route AS1, AS3 –AS1 will not accept AS2, AS1, AS3 from AS2
20 Jim Binkley however - regarding policy routing u routing choices may be made on basis of "policy" –policy mechanism not as flexible as arbitrary src routing, as a simplification for now, you can: –ignore routes or some routes from A –send all or some routes to B (or none) –policy based on IP address, AS number/path or Communities (sets of routes), and/or BGP attributes –and manual configuration choices about same
21 Jim Binkley NSFNET u as sole Inet backbone u way back when, got us thinking about this u Acceptable Use Policy: –not ok for business to use govt. funded net –therefore business had to somehow tunnel around it u another possibility: don't make silly rules
22 Jim Binkley policy routing and BGP u we might distinguish policy-in-the-large and policy-in-the-small u e.g., IDPR was after end to end policies –not clear how to administer though (more lawyers) u BGP can't do that, so let's admit it and move on u your policy affects this router or your set of routers in your AS –you can only hack at other people's policies... u essentially manual and locally configured
23 Jim Binkley BGP policy is hop-by-hop (mostly) u an example of something you can't do you zena sally ASen oldscratch sweetangelsally can choose to not advertise you r routes to sweetangel or just have a static route to oldscratch for zena... you cannot control sally
24 Jim Binkley one other little item - asymmetric routes u in the preceeding slide we wanted to route thru sweetangel to zena u but got routed thru oldscratch u zena might have a default route thru sweetangel u thus paths could be asymmetric u this is not unusual
25 Jim Binkley Cisco scheme for how BGP routing proceeds (overview) u we get UPDATES (new or withdrawals) –we subject them to input policy configuration u survivors are stored in routing database –IETF term is Routing Info Base (RIB-IN) u decision process chooses "best" (acc to policy) u puts chosen best route in routing table –in theory, BGP routing table –subject these routes to output policy config u advertise those routes put in routing table to peers
26 Jim Binkley picture of BGP router process update may be modified/deleted by input filter RIB (> 1 route to x) decision process (choose 1) rt. tab. update munged by output filter single route to X
27 Jim Binkley important principle u BGP does hop by hop routing, therefore u we only advertise what we use u if we put it in our routing table –we MAY advertise it, depending upon output filtering u if we receive a routing withdrawal and it is –in our RIB only, what do we do? –in RIB and routing table, what do we do?
28 Jim Binkley assume as4, lose as2 or as3 as 1 as 2 as 3 as 4 rib rt. table 2/1 to 1 via 3 3/1 1. if as2 lost, we don't change routing table, no update 2. if as 3 lost, we have 2/1 in rib, change routing table, to 1 via 2, send update
29 Jim Binkley convergence with BGP means what? u not all RIBs are the same for sure –(different vectors, and other attributes) u same set of IP dsts, with at least one path, and one routing table entry –which may differ from R to R –important assumption: policy does not lead to partition of Internet (has happened) u policy can cause differences of course u flapping - route goes up/down at high frequency, leads to mucho BGP updates
30 Jim Binkley stupid BGP mistake AS transit Sally stubby bob if sally sends us full Inet routing table, what should we send her? what should we not send her? entire set "bobnet" ip = 131.252/16!
31 Jim Binkley summary: some update rules u we only advertise what we put in our routing table u updates are not refreshed –RIB entries do not time out u BGP only talks when something changes –updates are adds or withdrawals or some other change based on attributes u any RIB change drives the decision process u we exchange routing tables at boot u all of above subject to policy configuration, in/out
32 Jim Binkley IBGP/IGP issues: 1. synchronization u consider transit AS: EBGP route updates multi-hop IBGP what happens if IBGP delivers route for dst X to partner Z, but transit IGP has not converged? X Z
33 Jim Binkley IGP sync: u answer: we must somehow make sure that the IGP has converged before u EBGP is advertised to Z –remember I send you routes, you send me data u why? because IBGP is multi-hop, and interior router might not know path to X –black hole... u in general: don't send route until you can forward...
34 Jim Binkley how do we solve this problem? u 1. we could wait for IGP synchronization –e.g., EBGP router to Z can't advertise until IGP "route tag" shows up and –local IGP routing table shows path to X u acc. to Moy, transit AS do not want to dump full Inet routing table into IGP –e.g., OSPF on all routers does SPF calculation over and over again during route flap –you have >= 150k routes == ouch
35 Jim Binkley plan B, C, D, etc. u 2. all internal routers use IBGP (aka use BGP...) –with no synchronization –IBGP is IGP (deal with it...) –IGP basically gets you to next hop –wait: we have a potential N**2 problem … u 3. or possibly default route plus a few IGP routes leaked in (if possible) u 4. or route recursion … u 5. or simply tunnel over internal routers – can use logical circuits courtesy of MPLS or possibly vlans courtesy of Ethernet (or ATM circuits)
36 Jim Binkley common implementation idea u combine next-hop bgp attribute with u recursive routing table lookup –(similar to an IPIP tunnel but not the trick) u control: next-hop for ip X is router Y u routing back: next-hop is NOT directly connected router, therefore must "tunnel" back to Y
37 Jim Binkley recursive lookup picture BR1 BR2 1/8 126.96.36.199 Internal IGP/IBGP mesh 1/8 next hop is 220.127.116.11 (BGP attribute) 22.214.171.124 (internal) How do I get to 1/8 via 22.214.171.124? To 126.96.36.199 via 184.108.40.206...
38 Jim Binkley stub AS might be implemented like so: ISP #1 ISP #2 IBGP internal OSPF routing domain default route into OSPF default route into OSPF + maybe other nearby routes therefore default routes can help out in this case
39 Jim Binkley circuit or logical circuit u consider transit AS: EBGP route updates this is not a router but a switch X Z IBGP from BG to BG MPLS ATM frame-relay, maybe even Ethernet
40 Jim Binkley MPLS – very short intro u ATM allows circuits across switches multiplexing and circuit paths based on tags (small ints) in cells setup manually or dynamically (signaling protocol)
41 Jim Binkley Multi-protocol layer switching u logically between L2 and L3 u not L2 specific u can setup signal path u basically "tunnel" across a domain u offers possibilities for traffic shaping, QOS, VPNs, and more or less making L2 link go further u and has tags like ATM
42 Jim Binkley another IBGP issue u in-order to remain loop free, all AS internal routers must peer –same AS, we can't add it as a prefix u call this full-mesh IBGP u in large AS, this leads to manual configuration nightmare –all those TCP connections, N**2 more or less u thus notions of route reflectors, route confederations to improve intra-AS scalability
43 Jim Binkley full meshed IBGP must have peer connection for all peers
44 Jim Binkley mechanisms exist for making IBGP mesh more scalable u route confederation notion: –break single AS up into multiple internal AS –tie together with EBGP connection –to outside still appears as one AS –each internal group must have fulled meshed IBGP –next-hop, MED, and local preference attributes important
45 Jim Binkley route reflector u in addition to confederation, we may have route reflector (internal route server) u AS divided into clusters u each cluster has route reflector u route reflector "reflects" updates to internal cluster peers, thus no full mesh in cluster u clusters have IBGP connection between them - need complete connections here
46 Jim Binkley note re IBGP and attributes u AS_PATH is NOT incremented, –therefore must manually prevent loops u NEXT_HOP is not touched either. –it's the way out of the AS with IBGP –need recursive lookup to send pkt in direction of next-hop
47 Jim Binkley the protocol u open/close state machine as virtual circuit u TCP, port 179 u TCP pros –we don't have to resend or be reliable –don't care about fragments/resends/loss, TCP job –we can be message-based, variable length »BGP is TLV protocol design more or less –hence updates can be incremental u BGP is stateful due to TCP and RIB both
48 Jim Binkley TCP cons u we need our own keepalive as we cannot rely on TCP keepalive –or assume all link hw has up/down indication u TCP might slow-down due to congestion control –doesn't make sense to have BGP as control slow-down in the face of "real video" ??? u BGP level security would not prevent TCP level attacks –e.g., you have authenticated BGP, you face TCP sequence number spoofing
49 Jim Binkley BGP message types u 1 OPEN - start of connection u 2 UPDATE - set of route withdrawals or new routes u 3 NOTIFICATION - fatal error or close u 4 KEEPALIVE - I'm still here partner u all messages have common header u messages overlayed on TCP byte stream
50 Jim Binkley header u all BGP messages started with 19-byte fixed length header u marker can be used for checksum (e.g., MD5) or simply as framing/redundancy check (must have expected value). u e.g., if no authentication, then marker is all 1s. u length, acc. to RFC 1771, 19 to 4096 16 byte marker length (2 bytes) type (1 byte) (1,2,3,4 for values)
51 Jim Binkley open message version=4 AS number (2 bytes) hold time (2) BGP Identifier (4 bytes) auth code optional authentication data (code may be optional too) header...
52 Jim Binkley open u post connect, 1st send OPEN, get KEEPALIVE back if OK, else NOTIFICATION u hold time - sender states in seconds time in which peer must send keepalives –or updates, but if no updates, then keepalives u ID is a local IP address u it is possible that both BGPs will connect at the same time –if so, one connection closed, winner has higher IP in ID
53 Jim Binkley multi-protocol BGP note u note that open takes options u multiprotocol BGP can thus be negotiated with these options: –capabilities negotiated at OPEN –includes MPLS, Multicast, IPv6 –attributes for multicast NLRI also exist u this allows BGP to do more than IPv4
54 Jim Binkley updates u contain two parts (either of which may not exist), more or less: u (withdrawn IP nets (possibly > 1), one path) u however one path consists of u (path attribute length, attributes, NLRI) u the path is in the attributes u NLRI - network layer reachability information –set of possibly > 1 IP addr/masks (lengths really) –therefore these NLRI share the attributes
55 Jim Binkley update withdrawn length 2 bytes variable set of withdrawn routes path attr length 2 bytes variable set of path attributes variable amount of NLRI header...
56 Jim Binkley update, cont. u withdrawn, aka unfeasible –if len = 0, there are none u routes expressed in length/prefix form –length is 1 byte long, comes first –e.g., 8/64 would be 188.8.131.52/8 –netmask, but actually contiguous prefix –both withdrawals, and NLRI like this u withdrawn routes - routes to toss out of RIB –may or may not affect routing table
57 Jim Binkley path attributes are complex part u encoded as triple (type, length, value) u type actually (flags as byte, type code) u flags = –optional - else mandatory (msg must contain it) –transitive - pass it along, even if unrecognized –partial - set to 1 if unrecognized transitive anywhere in path –extended - used to indicate length 0..N
58 Jim Binkley path attributes thus have 4 categories u 1. well-known and mandatory –well-known, all implementations must do it u 2. well-known and discretionary u 3. optional transitive u 4. optional non-transitive u thus we can have attributes that may not be known to all implementations AND passed on or dropped (non-transitive)
59 Jim Binkley before we nerd out on attributes u bottom line: attributes are one more input for policy u therefore policy is a function of –attributes in BGP updates –local rules about things like IP dst (NLRI), AS paths (one attribute among many), communities (another attribute) –and other possible manual config items, e.g., you can ignore an attribute
60 Jim Binkley attribute types u ORIGIN/mandatory u AS_PATHmandatory u NEXT_HOPmandatory u MULTI_EXIT_DISC (aka MED) u LOCAL_PREF u ATOMIC_AGGREGATE u AGGREGATOR transitive u COMMUNITY transitive u ORIGINATOR_ID u CLUSTER_LIST –about 2 for route reflection u DPAtransitive u ADVERTISER u RCID_PATH –above 2 for route server u more may be defined u note: not all explained here!!!
61 Jim Binkley attributes explained u ORIGIN may be {IGP, EGP, or INCOMPLETE) –historically used to indicate EGP origin during EGP to BGP transition –IGP means BGP injected route –INCOMPLETE means route redirection »static or OSPF or something –created by route originator –can make policy decisions, (IGP better than INCOMPLETE)
62 Jim Binkley attributes, more u AS_PATH is required u if IBGP, then NULL, else prepend own AS u path is a list of segments (ASen) expressed as TLV u Tag is either –AS_SET - unordered, i.e., not a sequence –AS_SEQUENCE, ordered u aggregation can muddy the path; e.g., –1, as_set = 2,3 as path is 1,2 or 1,3
63 Jim Binkley attributes never end u NEXT_HOP, router A on this link suggests using router B as next hop instead of A u MED - AS 1 has two points of attachment to you, the MED indicates preferred path –it is a weight –lower value win u LOCAL_PREF BGP uses this to tell IBGP peer/s that it is best way to outside X –higher value wins
64 Jim Binkley MED picture 28.8k modem gigabit ethernet AS 1 has better med here you hopefully choose this path AS 2 AS 1 uses MED to tell AS2 what local link to use note: this is near-local attempt to influence another AS
65 Jim Binkley LOCAL_PREF AS X X is better this way X is not so hot this way...
66 Jim Binkley more attributes u AGGREGATOR - info only, AS X committed aggregation on this path u COMMUNITY - arbitrary routes grouped together as a set... call it a route-bundle –useful for policy (I will forward the state of Kansas, but not the state of Missouri) –often stripped at AS boundaries, even though transitive –allows you to use tags as opposed to addressing info
67 Jim Binkley community u predefined attributes include: no-export - do not send this to EBGP peers no-advertise - do not send this to anyone internet - send this to everyone (the uber- bundle) u E.g, an AS might distinguish between routes from UUNET, I2, and routes internal to itself, and tell its own customers which is which
68 Jim Binkley Cisco weight attribute u cisco-defined and local to a router, not BGP protocol u R1 recvs route X from R2 and R3 u if from R2, weight is 50 u if from R3, weight is 100 u bigger weight is put in routing table
69 Jim Binkley summary: attributes/plus Cisco weight u MED u LOCAL_PREF u Cisco admin. weight u COMMUNITY u AS_PATH u ORIGIN u NEXT_HOP
70 Jim Binkley notification error code error sub-code variable length data (deduce from hdr length) header (marker, length, type=NOTIFICATION)
71 Jim Binkley notification protocol u when? –error –e.g., holddown elapsed –or graceful close (on purpose) u result is peer connection is closed –errors are fatal u and hopefully log message... –oh admin - things are bad here...
72 Jim Binkley notification error codes (major, minor) codes u 1 - message header errors –(error = 1, sub-code=1), connection not synchronized –(1,2) - bad message length –(1,3) - bad message type u 2 - open message –(2,1) - bad version number –(2,2) - bad AS –(2,3) - bad ID –(2,4) - unsupported optional parameter
73 Jim Binkley notification errors, cont. u 3 - update message error –quite a few... problems with attributes –note (3,7), AS routing loop u 4 - hold timer expired u 5 - finite state machine error u 6 - cease (close... not really an error)
74 Jim Binkley keepalive from 1000 miles up u BGP messages only occur if there are routing topology changes u keepalives on link are how we learn about link failure –and are rather important –we may not be able to trust a specific kind of link to tell us (keepalive is sw fix on flaky hw) –we may not be able to trust TCP keepalive, therefore BGP does not use
75 Jim Binkley keepalive u nothing but (marker, length, type=KEEPALIVE) u in order to avoid connection failure u must send message or KEEPALIVE –within holddown time u zero holddown means no KEEPALIVES needed –perhaps we want to avoid link charges u keep in mind transport is TCP, therefore delay an be unpredictable –keepalive frequency > holddown time is good idea
76 Jim Binkley routing decision process u we have RIB (database) paths and other attributes u we must process them into routing table entries u the decision process is the algorithm here u logically we do the following (acc to 1771) –1. choose routes to advertise to IBGP peers –2. choose routes to advertise to EBGP peers –3. route aggregation and route information reduction u some function is applied to all possible candidate routes for IP dst X, highest preference wins
77 Jim Binkley condensed cisco algorithm u next-hop route must exist (may need IGP to provide it) u consider larger administrative weights first (Cisco weight) u prefer route with largest local preference, else if same prefer local originated u if none of above, choose shortest AS_PATH u prefer IGP over EGP (ORIGIN) –IGP better than EGP better than INCOMPLETE (which appear because of route redistribution) u prefer lowest MED metric u if MEDS same prefer EBGP over IBGP u else if tie, prefer lowest BGP ID
78 Jim Binkley basic Cisco setup u router bgp –network mask [route-map route-map-name] u Note: network injects local network into BGP, but does not specify which IP addr to use for peer connection –neighbor remote-as u Note: neighbor specifies peer and peer AS
79 Jim Binkley logical network layer - 2 EBGP peers AS 100 AS 200 dexter radia Inet (therefore dexter advertise 0.0.0.0 from static routes) subnet 215.16/28 subnet 215.32/28
80 Jim Binkley simple example - dexter u router bgp 100 –network 22.214.171.124 mask 255.255.255.240 –redistribute static –neighbor 18.104.22.168 remote-as 200 –default-information originate
81 Jim Binkley simple example - radia u router bgp 200 –network 220.127.116.11 mask 255.255.255.240 –neighbor 188.8.131.52 remote-as 100 u note: radia has IP address 215.18 and dexter has ip address 215.17 on shared 215.16/28 subnet
82 Jim Binkley some bgp tricks (cisco code not included) u 1. routing by input src net 1 net 2 net 3 net 4 AS me/myself /I we can route packets from net 1 to net 4, from net 2 to net 3 based in IP src address mapping
83 Jim Binkley ip src addr mapping u questions about previous slide: u why is such a routing policy "not normal"? u can you perform this trick for the AS "outer mongolia"; i.e., an AS arbitrarily far away?
84 Jim Binkley review 2 1-way paths u inbound traffic - depends on routes YOU SEND u outbound traffic - depends on routes YOU RECEIVE u it may not be that hard to advertise NET1 over LINK1 –and thus cause asymmetric routing as a form of load balancing
85 Jim Binkley AS_PATH manipulation u one possible way to influence an AS farther away u prepend your own AS > 1 time to a path you send out what is consequence of this routing-wise? AS ME/ME/YOU* AS ME/YOU* - what is consequence of this ?
86 Jim Binkley load balancing ?! u see Halabi for his discussion u define here as multiple paths at layer 3 to dst X u general remarks –possible, but remember two things –BGP is hop by hop - you have less knowledge of net farther from home (ahem. KISS may apply) –routing is two 1-way problems –Asymmetric routing may/may not be ok - your call u you cannot load balance without redundancy - and asymmetric routing may be part of picture
87 Jim Binkley Cisco routers u automatically load-balance if –same router, two links to same IP prefix –what can you say about the nature of those two links? (similar bandwidth pro) –this info is not extended into IBGP, i.e., only one route is forwarded –use maximum-paths BGP command
88 Jim Binkley hot-potato routing u in decision process, (after EBGP over IBGP) u we can prefer IGP (OSPF) shortest path u this means data packet goes shortest path internally to get OUTSIDE of us u hot-potato -> in some sense spit packets out of AS the fastest possible way
89 Jim Binkley some BGP problems u scalability of transit system with IBGP –and IGP issues therein –we covered this one already (confed/reflector) u flapping (up/down/up/down...) u misconfigured junior partner –howzabout "routed -g" globally? u congestion leads to TCP backoff u security
90 Jim Binkley flapping u small fraction of routes have been known to cause many updates to "flood" BGP net u call this "route flap" –route UP, then DOWN, then UP, DOWN, etc. u basic idea: if path changes too fast, we will suppress sending updates about –aka holddown technique –a path may have a weight associated with it, penalized over time for more flapping u Cisco calls anti-flapping config route dampening
91 Jim Binkley BGP misconfigurations u small AS could simply announce that it is MIT (BGP equivalent of routed -g...) –and suck local MIT packets towards it u April 1997, small Virginia ISP more or less announced it was Inet Center (it wasn't) u such incidents have led to desire to sanity check and/or globally list policy u btw: you can always use ACLs and MAPS to sanity check your (small) neighbors
92 Jim Binkley Inet Routing Registry effort (www.irr.net) u global registry in multiple distributed databases u continues earlier RADB (www.radb.net) effort u RIPE-181 policy language evolved now into RPSL - Routing Policy Spec. Language – (see RFC 2650 for examples) u policy language describes routes/AS #s send/received by a given AS number –as well as POC (point of contact) –import from AS1 accept ANY –import from AS2 accept only AS2
93 Jim Binkley criticisms u garbage-in, garbage-out –admins may not keep up u accept ANY isn't terribly useful –big ASs can however enforce check on small AS u Bates/Bush/Rekhter/Li have suggested that routing policy be made available in DNS tree –could be administered locally –DNS could be made secure with signatures
94 Jim Binkley BGP congestion and other problems u 1997 SIGCOMM/Labovitz paper found –more Inet updates in BGP than needed –many were due to bugs in hw/sw u 1998 study repeat found improvement but –possible problems due to congestion –TCP would backoff –causing BGP timer failures, reboots, lost packets, BGP update spikes, cascading failures
95 Jim Binkley BGP security u in theory, BGP marker designed for MD like MD5 or the like u but, attack could be aimed at underlying TCP therefore we must protect TCP too –spoof TCP sequence number and do what? –DOS - send RESETs –or inject fake route info for MIM attack? u protection schemes therefore?
96 Jim Binkley possible fixes u RFC 2385 - TCP option using MD5 signature –point is sign both TCP and BGP data u another possibility - use IPSEC –possibly with AH only –end to end between the two peer routers, not tunnel mode
97 Jim Binkley BGP and AS numbers u how do you find AS info? e.g., using ARIN –# whois -h whois.arin.net "a " –note: whois –h whois.arin.net ? u e.g., PSU AS number u Portland State University (ASN-PDXNET) –Autonomous System Name: PDXNET –Autonomous System Number: 6366 u as found in ARIN u query -- see if you can find OGI AS #? u query #2 -- what if you have an AS_PATH... see if you can decode it; e.g., 3701/14262/11964
98 Jim Binkley BGP and Inet exchange connectivity u upstream connectivity may be defined as follows: –transit – you buy full connectivity from an ISP »therefore you are an end customer usually –public peering – ISP1 and ISP2 give each other BGP info about their own customers »not the Inet as a whole »probably done in a public way at an exchange/NAP –private peering – at an exchange, or NAP two ISPs have a private circuit and exchange whatever they exchange
99 Jim Binkley ISP Tiers u Tier 1 – the big ISP players –national backbone –does not purchase transit u Tier 2 – –national backbone –BUT does purchase some transit u Tier 3 –regional or local network –mostly transit, may have some peering
100 Jim Binkley this implies various levels then for exchanges u private peering in 8 US locations called the "default-free" zone u NY, Wash DC, Atlanta, Chicago, Dallas, LA, Seattle, San Jose u nevertheless there exist MAEs, IXPs, NAPs –metropolitan area exchanges –inet exchange points and network access points –these are in some sense public peering points
101 Jim Binkley general study question u BGP peering means exchange of AS information –large want to charge small for this of course –can involve lawyers, contracts, etc. u see what you can find out about peering on the Inet –including structures of NATs/MAEs –how would you design a large peering network? (never mind the lawyers...)
102 Jim Binkley more picky study questions u what kinds of BGP protocol messages exist? u what are the pros/cons of using TCP as a transport? u what security mechanisms can be used with BGP? u explain BGP and policy - how can an AS control route dissemination? u what is the MED attribute? what is it good for? u what does hot-potato routing mean? really? u why does AS_PATH protect BGP against looping?
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O'Reilly's Fluent Conference
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subset: commoncrawl


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Witch Magic Spells in Aurora, CO
In light and in love, enter! My name is Phelan, I am a white witch and root worker located in Atlanta, GA. I have clients from all over the world and have worked with them in Aurora, CO or San Antonio, TX, magic knows no boundaries for it to bring magical change to your life; magic is energy capable of reaching anybody, anywhere; therefore, where you live in conjunction with me is unimportant, but if you live in Atlanta we can arrange a meeting for a consultation or a psychic reading. Simply create an account to contact me online or call me at 678-918-3333, I can also assist you with powerful protection amulets, powerful amulets to increase love in your life, how to make a protection amulet or root bag.
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The solar homeowner has enough challenges at his or her doorstep without yet another obstacle. Some utilities have welcomed solar as a growing part of their energy portfolio—and yet still others see solar as a threat, to be stopped at any cost. This blog entry is about the latter sort. You probably have a hard enough time in reading your electricity bill—do the utilities do that on purpose? Try finding the average rate utility customers are paying in your region. You may be lucky and the utility may provide good access to that data—or not. If they can obscure the information and get away with it, who wants to sift through all of the arcane data? And that is the backdrop to the new net metering battles playing out throughout the country.
Posts Tagged 'solar energy'
Utilities Double Dipping into Net MeteringFriday, October 29th, 2010
Clean Energy Advocates Regrouping and Waiting for the Election ResultsFriday, October 22nd, 2010
We went to a reception by the Clean Economy Network last night—we had a chance to meet with lawyers and lobbyists, financial analysts, and even a few solar energy installers. We got a good review of industry trends and some of the upcoming challenges from Reed Hundt, CEO of the Coalition for Green Capital and Ethan Zindler, Head of Research at Bloomberg New Energy Finance. There is obviously keen interest in renewable energy these days. Take a look at the news article we posted today on some of the latest optimistic trends in the solar industry. Support for solar energy is up—right across the board, regardless of party affiliation or geography. Some want to reduce the threat of global warming, and some want to create jobs, and still others simply want to do their part to save energy. The solar energy industry is optimistic that the residential PV market will continue to expand. At the reception, despite some of the hopeful signs, there were some long faces in the room.
The Senate to Climate Change Advocates: Drop DeadTuesday, July 27th, 2010
The death of the energy bill has left a lot of people pointing fingers at each other, and a lot of people wondering if we cannot now take action on climate change, then when—and by whom? A Washington Post article today identifies some very unhappy House Democrats who went out on limb last year to support the energy bill and combat climate change. They now understandably feel hung out to dry. I think that the New York Times columnist Paul Krugman best summarizes the events of the last few days: "Greed, aided by cowardice has triumphed."
White House Correspondent Paul Brandus Meets with SolarTownThursday, July 15th, 2010
SolarTown met with Mr. Paul Brandus, a White House correspondent with a huge interest in green issues. Brandus is a strong advocate of renewable energy, relating a story on how he personally asked President Obama when solar panels would be installed on the White House, on three separate occasions. Although no solar modules have yet to grace the President's residence, Brandus expressed his desire to see the 132 rooms of the White House heated by the rays of the sun and the power of the wind, calling the act a great symbolic value to the nation. Incorporating solar and other forms of alternative energy into the lives of Americans is still a major challenge. Interest in environmental-related topics is only illustrated when major catastrophes such as the BP oil spill occurs. After the disaster dies down, the interest responds accordingly. Brandus believes that it will take awhile for solar and renewable energy to fully assimilate into everyone's lives.
Is Solar Energy Back on the Agenda?Friday, June 25th, 2010
"The time to embrace a clean energy future is now," said the President during his talk on the BP oil spill earlier this month. For much of the past year, the nation's energy policy has played second fiddle to , well, everything else, but primarily health care and most recently financial reform. Deadlines have come and gone, and with the mid-terms elections around the corner, it is hard to see how Obama will pick a rabbit out of the hat and push the energy agenda forward.
What is clear is that as states and local governments are cutting back on their solar energy programs, just at the time when the solar industry needs this support the most. The Maryland program cut its rebate program with only a few days notice. Take a look at our SolarTown news stories to read about some of the states that are throwing their renewable energy programs to the wind in an effort to close budget gaps.
Earth Day 2010: Turn Off the Lights!Thursday, April 22nd, 2010
The school where my kids go encouraged all students to walk to school today. We usually drive them to school, so we had to get them up and out of the house a little earlier this morning. I got up and went downstairs to see if they had already gotten up and saw that all of the lights in the kitchen were on and all of the lights in the den were on and all of the lights in the TV room were on—and no sign of my kids who were still upstairs watching Mythbusters on a laptop. Now you have to realize that my kids are generally very environmentally conscious and very supportive of SolarTown's mission to promote solar energy. But there sometimes is this huge gap between your views and beliefs and taking action on your beliefs. My son is a hard core believer but a less than hard core doer. And that is the challenge we have on Earth Day: how do we move from what we believe to taking actions, even modest ones like turning off the lights when we are out of the room
Reenergizing Solar in the US: A National Security PriorityMonday, April 19th, 2010
Ambassador Stuart Eizenstat gave the keynote address at today's George Washington University Solar Institute Symposium here in Washington, D.C. Eizenstat, domestic policy adviser to President Jimmy Carter, was there when Carter installed solar panels on the White House in the late 1970s, when the promise of solar seemed bright. Eizenstat recounted that the "momentum waned" and the solar panels were "dismantled by the next president." Eizenstat laid out a powerful argument for solar: national security.
Solar Economic Incentives: Fragile as the WindFriday, March 5th, 2010
The solar industry applauded when the 30% federal tax credit was extended to 2016 and the legislation lifted the cap. The reason of course is that for all intents and purposes, the solar industry is just emerging and needs substantial support, and the stability in the incentives provides this support. But now one important part of this program, known as the treasury grant program, has been placed in jeopardy. Four senators released a letter in which they urged the Obama Administration to suspend this program until the legislation could be amended to allow only for clean energy projects "that preserve and create jobs in the United States." You can read the full text of the letter here. The abrupt fits and starts of incentive programs, and not just this federal program, only serve to stall the march to solar.
The Solar GenerationTuesday, March 2nd, 2010
Buried on page 20 of our local paper was a news item "Students push solar for NCS." The National Cathedral School may not qualify as you your average American school. (For those of you not in the know, NCS is a private school home to some of sons and daughters of the elite of the Nation's Capital.) But what is going on at NCS may be a glimpse of what the future holds. The article in the Northwest Current chronicles how NCS is now planning on installing 32 solar panels on a century old (read historical) building at NCS—due to the insistence and perseverance of two students at NCS, Charlotte Zimmerman and Christina Boulineaux. The two raised $20,000 and even interviewed solar contractors so that they could place these solar panels on NCS.
Financing, Incentives and the Future Forward for SolarFriday, February 5th, 2010
The Renewable Energy Technology Conference (RETECH 2010) here in Washington, D.C. convened over the last couple of days. I am sure that there will be much written about the conference that concentrated on strategic issues, finance and incentives for renewable energy. The Conference highlighted many of the common challenges faced by renewable energy projects, regardless of whether they are solar PV, biomass, wind or geothermal. There were some recurrent themes at many of the sessions that I attended on federal and state incentive programs, local programs, and financing of solar energy products.


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Is St. John the Baptist Parish Church incorrect or missing key business information? Update your Hotfrog listing today.
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Hotfrog Philippines provides information regarding St. John the Baptist Parish Church in Bacolod Negros Occidental. St. John the Baptist Parish Church is located at Bacolod Negros Occidental 6100 and provides Churches services. Contact them on (034) 444 1870.
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Hit the brakes… Did David Ellison, co-producer and Skydance CEO, just spill some important casting news about Top Gun 2? Tom Cruise back as Maverick? Sure Hollywood, I'll take some more nostalgia.
Here's the deal. Top Gun has had a rumored sequel since around 2010. The 1986 film served as Tom Cruise's breakout hit, and fans have wanted a sequel ever since. In 2012, Cruise scouted locations for a potential sequel with the film's director Tony Scott. Unfortunately, Scott passed away in August of that year.
Fast forward to today and you have David Ellison speaking at a press event Friday for the upcoming Terminator Genisys. Here's the quote that is lighting up the Internet, as reported by Collider:
"Justin Marks is writing the screenplay right now. He has a phenomenal take to really update that world for what fighter pilots in the Navy have turned into today."
"There is an amazing role for Maverick in the movie, and there is no Top Gun without Maverick, and it is going to be Maverick playing Maverick," he continued. "It is I don't think what people are going to expect, and we are very, very hopeful that we get to make the movie very soon. But like all things, it all comes down to the script, and Justin is writing as we speak."
Can you be any more cryptic? Maverick is going to be Maverick in a film based on maverick fighter pilots who start acting all mavericky. He could sub for Sarah Palin any day of the week.
Is Tom Cruise going to be in Top Gun 2? The answer is we don't know. Cruise hasn't commented on it, and the screenplay isn't even complete.
Top Gun 2 Details
Without a screenplay, we have to work off quotes of producers and directors. In 2014, Jerry Bruckheimer spoke to HuffPost Live about the possible plot of the movie.
"The concept is, basically, are the pilots obsolete because of drones. Cruise is going to show them that they're not obsolete. They're here to stay."
So, it's like if Stealth was actually a good movie?
If Tom Cruise was to reprise his role, Ellison was quoted by Collider as saying the actor would want to keep with his crazy ways. Cruise would "100 percent going to want to be in those airplanes shooting it practically."
Yeah, I'm sure the Navy is 100 percent on board with handing over the keys to an F-35C.
In addition to Maverick going ballistic in Top Gun 2, Bruckheimer talked to Bloomberg about the potential film.
"Technology has changed obviously since we made the first one. So, I think we're going to take advantage of what the world is like today, you know with the drones really kind of taking over in a lot of our wars…Is the pilot obsolete? No, I don't think so…we're going to hopefully highlight both worlds."
Lots of rumors, a David Ellison trying to fit the word maverick in every sentence and that's about it.
Still, give us Top Gun 2. Hollywood gives everything else a sequel. Top Gun needs a wingman.
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Turner's Garage Doors
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Garage Door Motor Installs Who has time these days to stop the car and go out in the rain just
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Mary Kay Andrews
Great summer books need plenty of romance, scandal and gossip. Mary Kay Andrews's Spring Fever has all of that and more. The New York Times best-selling author of Summer Rental brings readers a tangled love story set in a small Southern town. Protagonist Annajane Hudgens thinks she's over her ex-husband, Mason Bayless, and goes to his wedding as a means of closure. Once there, she realizes she hasn't moved on quite as much as she thought. Will Annajane's decision to remarry and move to Atlanta put an end to her feelings for Mason or only make her long for him more? 6:30 p.m. Murder by the Book, 2342 Bissonnet. For information, call 713-524-8597 or visit www.murderbooks.com.
Fri., June 22, 6:30 p.m., 2012
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Givenchy Very Irrsistible Eau de Toilette 50ml Gift Set. Very Irrsistible Givenchy`s floral notes centre around a plethora of roses. Its central floral harmony is made up of five Rose notes: Daring Peony, Spontaneous Fa... show more
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Click here to see the full line of AnneMarie Borlind Beauty Essentials Series.
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3 G Corporation (Pty) Ltd
cleaning, Pre Occupation Cleaning, After Party Cleaning
After a long night of fun, the last thing you want to do the next morning is clean your home. Instantly book an 3 G Corporation after party cleaning service – so you can kick back and relax!
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Impact Rugby
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A good Rugby Jerseys outfit requires many different elements. Firstly, you have to think about what specific sport you are playing as quality Rugby League Jerseys is designed with a specific sport in mind.
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Rugby Headgear is a necessary for preventing a serious damage to the brain. The damage could occur abruptly, following a
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Impactrugby offer a complete range of off & off field clothings like Rugby League Jerseys, Rugby Kit, headgears, Rugby Teamwear,
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Is Yvonne S School Of Motoring incorrect or missing key business information? Update your Hotfrog listing today.
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Hotfrog Ireland provides information regarding Yvonne S School Of Motoring in Mullingar Westmeath. Yvonne S School Of Motoring is located at Mullingar Westmeath and provides Education services. Contact them on 087 623 6033.
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Forest Park Mullingar Business Park Mullingar Westmeath
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Harriet S.MeyerMD, Contributing EditorJonathan D.EldredgeMLS, PhD, Journal Review EditorRobertHoganMD, adviser for new media
Not Available
This excellent book provides a comprehensive review of the medical implications of working in a compressed air environment. Unlike most books on the bends, which stress pathophysiology and treatment options, this one emphasizes historical accounts of physicians, scientists, and engineers struggling to understand this unique malady.
The book is comprehensive: it begins with the origin of the atmosphere billions of years ago and concludes with a discussion of new advances in the use of fluorocarbons for liquid breathing. In my opinion, the heart of this book is the series of chapters on the use of compressed air in the building of several major bridges and tunnels. Individual chapters are devoted to the construction of the St Louis Bridge, the Brooklyn Bridge, and major tunnel projects around New York city. Each project was beset with problems with decompression sickness, and each resulted in new knowledge and policies to prevent the disease. Dr Phillips does not simply give a chronology of events, but also provides a detailed discussion of the thought processes involved in solving the mystery of why otherwise healthy bridge and tunnel workers sometimes developed serious and occasionally fatal symptoms following their work shifts. Of course, the physicians and scientists who have been closely associated with the bends are all well represented, including Boyle, Triger, Pol and Wattelle, Bert, Haldane, Behnke, Kindwall, and Lambertson.
The BendsThe Bends: Compressed Air in the History of Science, Diving, and Engineering. JAMA. 1998;280(7):666-667. doi:10.1001/jama.280.7.666-JBK0819-4-1
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H&R BLOCK, Finance & Taxation, Other Financial Services, listed under "Finance & Taxation, Other Financial Services" category, is located at 90 Executive Dr, Ste C Parris Island SC, 29905 and can be reached by 8433795255 phone number. H&R BLOCK has currently 0 reviews.This business profile is not yet claimed, and if you are the owner, claim your business profile for free. If you are not the owner you can invite this business to join by email or by phone.Browse all Finance & Taxation, Other Financial Services in Parris Island SC. Discover census data for Parris Island, SC.
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Chaotic Love Poems Trailer (2015)
08 October 2015 90 mins
A cheerful yet serious Indonesian Romeo and Juliet. A boy and a girl from the same district, but with difficult childhoods and other reasons not to acknowledge their love. Through the colourful and musical retro style - the 1970s came late to Indonesia - shines a chaotic political and social era.
Watch the official Chaotic Love Poems 2015 trailer in HD below or find more Chaotic Love Poems videos on Vidimovie.com.


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ISBN/ASIN: 9781555582630 | 2002 | English | pdf | 217/217 pages | 3.00 Mb
Publisher: Digital Press | Author: Jeffrey Peel (Auth.)
''I have long maintained that in a global market liberalized by free trade policies and advanced communications technology, there remains just one powerful regulatory forcethe customer. In this book, Jeffrey Peel has taken a close look at customer relationship management from the perspective of large distributed companies. This is a novel approach, not really covered by dot-com/IT-based definitions. The refreshing difference is that Peel appears to understand the difficulties and suggests practical methods to do things better.''Lord Marshall of Knightsbridge, Chairman, British Airways Plc ''In this book, Jeff Peel combines the deep insights of an experienced market researcher with the practical understanding of how technology can be applied to CRM to provide a truly original work. He provides a wholly new focus on how CRM impinges on marketing processes, which provides a particular challenge for marketeers and CRM practitioners to review the way they look at their separate disciplines. This book is for those marketeers, CRM practitioners, students, and academics who want to challenge the established preconceptions of what CRM is about.''Peter Hutton, Deputy Managing Director, Market & Opinion Research International (MORI), London