@@ -248,12 +248,12 @@ def snmpwalk(dst, oid="1", community="public"):
     try:
         while True:
             r = sr1(IP(dst=dst)/UDP(sport=RandShort())/SNMP(community=community, PDU=SNMPnext(varbindlist=[SNMPvarbind(oid=oid)])),timeout=2, chainCC=1, verbose=0, retry=2)
-            if ICMP in r:
-                print(repr(r))
-                break
             if r is None:
                 print("No answers")
                 break
+            if ICMP in r:
+                print(repr(r))
+                break
             print("%-40s: %r" % (r[SNMPvarbind].oid.val,r[SNMPvarbind].value))
             oid = r[SNMPvarbind].oid
             
## This file is part of Scapy
## See http://www.secdev.org/projects/scapy for more informations
## Copyright (C) Philippe Biondi <phil@secdev.org>
## This program is published under a GPLv2 license

"""
SNMP (Simple Network Management Protocol).
"""

from __future__ import print_function
from scapy.packet import *
from scapy.asn1packet import *
from scapy.asn1fields import *
from scapy.asn1.asn1 import *
from scapy.asn1.ber import *
from scapy.sendrecv import sr1
from scapy.volatile import *
from scapy.layers.inet import UDP, IP, ICMP

##########
## SNMP ##
##########

######[ ASN1 class ]######

class ASN1_Class_SNMP(ASN1_Class_UNIVERSAL):
    name="SNMP"
    PDU_GET = 0xa0
    PDU_NEXT = 0xa1
    PDU_RESPONSE = 0xa2
    PDU_SET = 0xa3
    PDU_TRAPv1 = 0xa4
    PDU_BULK = 0xa5
    PDU_INFORM = 0xa6
    PDU_TRAPv2 = 0xa7


class ASN1_SNMP_PDU_GET(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_GET

class ASN1_SNMP_PDU_NEXT(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_NEXT

class ASN1_SNMP_PDU_RESPONSE(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_RESPONSE

class ASN1_SNMP_PDU_SET(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_SET

class ASN1_SNMP_PDU_TRAPv1(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_TRAPv1

class ASN1_SNMP_PDU_BULK(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_BULK

class ASN1_SNMP_PDU_INFORM(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_INFORM

class ASN1_SNMP_PDU_TRAPv2(ASN1_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_TRAPv2


######[ BER codecs ]#######

class BERcodec_SNMP_PDU_GET(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_GET

class BERcodec_SNMP_PDU_NEXT(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_NEXT

class BERcodec_SNMP_PDU_RESPONSE(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_RESPONSE

class BERcodec_SNMP_PDU_SET(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_SET

class BERcodec_SNMP_PDU_TRAPv1(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_TRAPv1

class BERcodec_SNMP_PDU_BULK(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_BULK

class BERcodec_SNMP_PDU_INFORM(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_INFORM

class BERcodec_SNMP_PDU_TRAPv2(BERcodec_SEQUENCE):
    tag = ASN1_Class_SNMP.PDU_TRAPv2



######[ ASN1 fields ]######

class ASN1F_SNMP_PDU_GET(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_GET

class ASN1F_SNMP_PDU_NEXT(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_NEXT

class ASN1F_SNMP_PDU_RESPONSE(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_RESPONSE

class ASN1F_SNMP_PDU_SET(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_SET

class ASN1F_SNMP_PDU_TRAPv1(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_TRAPv1

class ASN1F_SNMP_PDU_BULK(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_BULK

class ASN1F_SNMP_PDU_INFORM(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_INFORM

class ASN1F_SNMP_PDU_TRAPv2(ASN1F_SEQUENCE):
    ASN1_tag = ASN1_Class_SNMP.PDU_TRAPv2



######[ SNMP Packet ]######

SNMP_error = { 0: "no_error",
               1: "too_big",
               2: "no_such_name",
               3: "bad_value",
               4: "read_only",
               5: "generic_error",
               6: "no_access",
               7: "wrong_type",
               8: "wrong_length",
               9: "wrong_encoding",
              10: "wrong_value",
              11: "no_creation",
              12: "inconsistent_value",
              13: "resource_unavailable",
              14: "commit_failed",
              15: "undo_failed",
              16: "authorization_error",
              17: "not_writable",
              18: "inconsistent_name",
               }

SNMP_trap_types = { 0: "cold_start",
                    1: "warm_start",
                    2: "link_down",
                    3: "link_up",
                    4: "auth_failure",
                    5: "egp_neigh_loss",
                    6: "enterprise_specific",
                    }

class SNMPvarbind(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SEQUENCE( ASN1F_OID("oid","1.3"),
                                ASN1F_field("value",ASN1_NULL(0))
                                )


class SNMPget(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_GET( ASN1F_INTEGER("id",0),
                                    ASN1F_enum_INTEGER("error",0, SNMP_error),
                                    ASN1F_INTEGER("error_index",0),
                                    ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                    )

class SNMPnext(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_NEXT( ASN1F_INTEGER("id",0),
                                     ASN1F_enum_INTEGER("error",0, SNMP_error),
                                     ASN1F_INTEGER("error_index",0),
                                     ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                     )

class SNMPresponse(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_RESPONSE( ASN1F_INTEGER("id",0),
                                         ASN1F_enum_INTEGER("error",0, SNMP_error),
                                         ASN1F_INTEGER("error_index",0),
                                         ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                         )

class SNMPset(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_SET( ASN1F_INTEGER("id",0),
                                    ASN1F_enum_INTEGER("error",0, SNMP_error),
                                    ASN1F_INTEGER("error_index",0),
                                    ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                    )
    
class SNMPtrapv1(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_TRAPv1( ASN1F_OID("enterprise", "1.3"),
                                       ASN1F_IPADDRESS("agent_addr","0.0.0.0"),
                                       ASN1F_enum_INTEGER("generic_trap", 0, SNMP_trap_types),
                                       ASN1F_INTEGER("specific_trap", 0),
                                       ASN1F_TIME_TICKS("time_stamp", IntAutoTime()),
                                       ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                       )

class SNMPbulk(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_BULK( ASN1F_INTEGER("id",0),
                                     ASN1F_INTEGER("non_repeaters",0),
                                     ASN1F_INTEGER("max_repetitions",0),
                                     ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                     )
    
class SNMPinform(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_INFORM( ASN1F_INTEGER("id",0),
                                       ASN1F_enum_INTEGER("error",0, SNMP_error),
                                       ASN1F_INTEGER("error_index",0),
                                       ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                       )
    
class SNMPtrapv2(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SNMP_PDU_TRAPv2( ASN1F_INTEGER("id",0),
                                       ASN1F_enum_INTEGER("error",0, SNMP_error),
                                       ASN1F_INTEGER("error_index",0),
                                       ASN1F_SEQUENCE_OF("varbindlist", [], SNMPvarbind)
                                       )
    

class SNMP(ASN1_Packet):
    ASN1_codec = ASN1_Codecs.BER
    ASN1_root = ASN1F_SEQUENCE(
        ASN1F_enum_INTEGER("version", 1, {0:"v1", 1:"v2c", 2:"v2", 3:"v3"}),
        ASN1F_STRING("community","public"),
        ASN1F_CHOICE("PDU", SNMPget(),
                     SNMPget, SNMPnext, SNMPresponse, SNMPset,
                     SNMPtrapv1, SNMPbulk, SNMPinform, SNMPtrapv2)
        )
    def answers(self, other):
        return ( isinstance(self.PDU, SNMPresponse)    and
                 ( isinstance(other.PDU, SNMPget) or
                   isinstance(other.PDU, SNMPnext) or
                   isinstance(other.PDU, SNMPset)    ) and
                 self.PDU.id == other.PDU.id )

bind_bottom_up(UDP, SNMP, sport=161)
bind_bottom_up(UDP, SNMP, dport=161)
bind_bottom_up(UDP, SNMP, sport=162)
bind_bottom_up(UDP, SNMP, dport=162)
bind_layers(UDP, SNMP, sport=161, dport=161)

def snmpwalk(dst, oid="1", community="public"):
    try:
        while True:
            r = sr1(IP(dst=dst)/UDP(sport=RandShort())/SNMP(community=community, PDU=SNMPnext(varbindlist=[SNMPvarbind(oid=oid)])),timeout=2, chainCC=1, verbose=0, retry=2)
            if ICMP in r:
                print(repr(r))
                break
            if r is None:
                print("No answers")
                break
            print("%-40s: %r" % (r[SNMPvarbind].oid.val,r[SNMPvarbind].value))
            oid = r[SNMPvarbind].oid
            
    except KeyboardInterrupt:
        pass


How about `r.show()`