Troubleshooting Border Gateway Protocol (BGP)
To troubleshoot with Border Gateway Protocol (BGP), you must gather information about the protocol and how it is functioning. As with other protocols, the two main sources of information are the show command and the debug command, so the place to start is by reviewing the show commands that you can use with BGP.
The BGP show command is surprisingly show ip bgp, which displays information about your router, including its Router ID and the networks that are visible with their metric, weight, and route flag. This command shows you whether the routes are internal (on the inside of your network) or stale (not updated recently and possibly down).
Notice that the RouterID is the address that was associated with the loopback interface, as with the OSPF protocol (covered in the previous chapter). Also as with the OSPF protocol, BGP uses the highest IP address of its connected interfaces as its RouterID, which you can force by using a loopback interface. To review both the OSPF protocol and how to configure the loopback interface.
Router2>enable Password: Router2#show ip bgp BGP table version is 2, local router ID is 192.168.255.254 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 192.168.6.0 192.168.1.2 0 0 100 i
The show ip bgp command has many options for viewing additional information. One of these options is neighbors. The command reveals the following information:
BGP version that is in use.
Neighbors that are visible. Although the command can be run with a neighbor specified.
BGP messages that have been seen.
BGP connections to other routers.
Event timer summary.
Router2>enable Password: Router2#show ip bgp neighbors BGP neighbor is 192.168.1.2, remote AS 100, external link BGP version 4, remote router ID 192.168.6.2 BGP state = Established, up for 00:11:11 Last read 00:00:11, hold time is 180, keepalive interval is 60 seconds Neighbor capabilities: Route refresh: advertised and received(old & new) Address family IPv4 Unicast: advertised and received Message statistics: InQ depth is 0 OutQ depth is 0 Sent Rcvd Opens: 1 1 Notifications: 0 0 Updates: 0 1 Keepalives: 14 14 Route Refresh: 0 0 Total: 15 16 Default minimum time between advertisement runs is 30 seconds For address family: IPv4 Unicast BGP table version 2, neighbor version 2 Index 1, Offset 0, Mask 0x2 1 update-group member Sent Rcvd Prefix activity: ---- ---- Prefixes Current: 0 1 (Consumes 48 bytes) Prefixes Total: 0 1 Implicit Withdraw: 0 0 Explicit Withdraw: 0 0 Used as bestpath: n/a 1 Used as multipath: n/a 0 Outbound Inbound Local Policy Denied Prefixes: -------- ------- Bestpath from this peer: 1 n/a Total: 1 0 Number of NLRIs in the update sent: max 0, min 0 Connections established 1; dropped 0 Last reset never Connection state is ESTAB, I/O status: 1, unread input bytes: 0 Local host: 192.168.1.240, Local port: 11001 Foreign host: 192.168.1.2, Foreign port: 179 Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes) Event Timers (current time is 0x75ECBF0): Timer Starts Wakeups Next Retrans 15 0 0x0 TimeWait 0 0 0x0 AckHold 14 8 0x0 SendWnd 0 0 0x0 KeepAlive 0 0 0x0 GiveUp 0 0 0x0 PmtuAger 0 0 0x0 DeadWait 0 0 0x0 iss: 2844915809 snduna: 2844916121 sndnxt: 2844916121 sndwnd: 16073 irs: 1529136828 rcvnxt: 1529137192 rcvwnd: 16021 delrcvwnd: 363 SRTT: 259 ms, RTTO: 579 ms, RTV: 320 ms, KRTT: 0 ms minRTT: 0 ms, maxRTT: 300 ms, ACK hold: 200 ms Flags: active open, nagle IP Precedence value : 6 Datagrams (max data segment is 1460 bytes): Rcvd: 20 (out of order: 0), with data: 14, total data bytes: 363 Sent: 25 (retransmit: 0, fastretransmit: 0), with data: 15, total data bytes: 311
Other show ip bgp options include the following:
Router2>enable Password: Router2#show ip bgp ? A.B.C.D IP prefix <network>/<length>, e.g., 220.127.116.11/8 A.B.C.D Network in the BGP routing table to display all All address families cidr-only Display only routes with non-natural netmasks community Display routes matching the communities community-list Display routes matching the community-list dampening Display detailed information about dampening filter-list Display routes conforming to the filter-list inconsistent-as Display only routes with inconsistent origin ASs injected-paths Display all injected paths ipv4 Address family ipv6 Address family labels Display Labels for IPv4 NLRI specific information neighbors Detailed information on TCP and BGP neighbor connections nsap Address family paths Path information peer-group Display information on peer-groups prefix-list Display routes matching the prefix-list quote-regexp Display routes matching the AS path "regular expression" regexp Display routes matching the AS path regular expression replication Display replication status of update-group(s) rib-failure Display bgp routes that failed to install in the routing table (RIB) route-map Display routes matching the route-map summary Summary of BGP neighbor status template Display peer-policy/peer-session templates update-group Display information on update-groups vpnv4 Address family | Output modifiers <cr>