'Change status of src <-> dst links.
src: node name
dst: node name
status: string {up, down}'

def configLinkStatus(self, src, dst, status):

    if (src not in self.nameToNode):
        error(('src    not    in    network:    %s\n' % src))
    elif (dst not in self.nameToNode):
        error(('dst    not    in    network:    %s\n' % dst))
    else:
        src = self.nameToNode[src]
        dst = self.nameToNode[dst]
        connections = src.connectionsTo(dst)
        if (len(connections) == 0):
            error(('src    and    dst    not    connected:    %s    %s\n' % (src, dst)))
        for (srcIntf, dstIntf) in connections:
            result = srcIntf.ifconfig(status)
            if result:
                error(('link    src    status    change    failed:    %s\n' % result))
            result = dstIntf.ifconfig(status)
            if result:
                error(('link    dst    status    change    failed:    %s\n' % result))
