Appendix A. The show ip bgp neighbors Display

This appendix explains the details of the large amount of information returned by the show ip bgp neighbors command. Some of the information is self-explanatory, and much of the information has been discussed in various chapters in this book.

Example A-1 shows a typical neighbor display, with each line numbered for easy reference. Table A-1 analyzes this sample display one line at a time.

Example A-1 Typical Display from the show ip bgp neighbors Command

 TeddyBear#  show ip bgp neighbors 10.100.1.1  1. BGP neighbor is 10.100.1.1,  remote AS 6500, internal link 2.  Member of peer-group Pooh for session parameters 3.   BGP version 4, remote router ID 10.100.1.1 4.   BGP state = Established, up for 00:04:06 5.   Last read 00:00:07, hold time is 180, keepalive interval is 60 seconds 6.   Neighbor capabilities: 7.     Route refresh: advertised and received 8.     Address family IPv4 Unicast: advertised and received 9.     Address family IPv4 Multicast: advertised and received 10.   Received 7 messages, 0 notifications, 0 in queue 11.   Sent 7 messages, 0 notifications, 0 in queue 12.   Route refresh request: received 0, sent 0 13.   Minimum time between advertisement runs is 5 seconds 14.  For address family: IPv4 Unicast 15.   BGP table version 1, neighbor version 1 16.   Index 1, Offset 0, Mask 0x2 17.   Pooh peer-group member 18.   0 accepted prefixes consume 0 bytes 19.   Prefix advertised 0, suppressed 0, withdrawn 0 20.  For address family: IPv4 Multicast 21.   BGP table version 1, neighbor version 1 22.   Index 1, Offset 0, Mask 0x2 23.   0 accepted prefixes consume 0 bytes 24.   Prefix advertised 0, suppressed 0, withdrawn 0 25.   Connections established 1; dropped 0 26.   Last reset 00:04:17, due to Address family activated 27. Connection state is ESTAB, I/O status: 1, unread input bytes: 0 28. Local host: 10.100.1.2, Local port: 11012 29. Foreign host: 10.100.1.1, Foreign port: 179 30. Enqueued packets for retransmit: 0, input: 0  mis-ordered: 0 (0 bytes) 31. Event Timers (current time is 0x3ABFA00): 32. Timer          Starts    Wakeups            Next 33. Retrans             8          0             0x0 34. TimeWait            0          0             0x0 35. AckHold             7          5             0x0 36. SendWnd             0          0             0x0 37. KeepAlive           0          0             0x0 38. GiveUp              0          0             0x0 39. PmtuAger            0          0             0x0 40. DeadWait            0          0             0x0 41. iss: 2227710177  snduna: 2227710341  sndnxt: 2227710341     sndwnd:  16221 42. irs: 1632859231  rcvnxt: 1632859395  rcvwnd:      16221  delrcvwnd:    163 43. SRTT: 540 ms, RTTO: 3809 ms, RTV: 1364 ms, KRTT: 0 ms 44. minRTT: 8 ms, maxRTT: 300 ms, ACK hold: 200 ms 45. Flags: higher precedence, nagle 46. Datagrams (max data segment is 536 bytes): 47. Rcvd: 11 (out of order: 0), with data: 7, total data bytes: 163 48. Sent: 14 (retransmit: 0), with data: 7, total data bytes: 163 TeddyBear#

Table A-1. Line-by-Line Explanation of show ip bgp neighbors Command Output

Line #	Syntax	Explanation
1	BGP neighbor is 10.100.1.1, remote AS 6500, internal link	This line is probably the most self-explanatory of the entire display. The IP address shown is the remote end point of the TCP connection between the BGP peers. The remote peer is in AS 6500, and the peer is internal ”that is, this is an IBGP connection.
2	Member of peer-group Pooh for session parameters	A peer group named Pooh has been configured on this router, and this neighbor is a member of the peer group.
3	BGP version 4, remote router ID 10.100.1.1	BGP-4 is running on this peering session. Recall from Chapter 2, "Introduction to Border Gateway Protocol 4," that BGP automatically negotiates the version with its peers, beginning with the most recent version supported. The BGP router ID of this peer is 10.100.1.1, which in this case is the same as the remote end point address ”due to the fact that the peering is between loopback interfaces, which also are used to determine the router ID. If the peering end points were between physical interface addresses, the router ID would likely not be the same.
4	BGP state = Established, up for 00:04:06	The neighbor state is established, which indicates a full adjacency . The session has been up for 4 minutes and 6 seconds.
5	Last read 00:00:07, hold time is 180, keepalive interval is 60 seconds	BGP last read a message from this peer 7 seconds ago. The holdtime is 180 seconds, and the keepalive interval is 60 seconds. These are the default values; recall from Chapter 2 that BGP neighbors can negotiate these times.
6	Neighbor capabilities:	The lines indented below this line summarize the capabilities of the peer.
7	Route refresh: advertised and received	The local router and the peer support the BGP Soft Reset Enhancement. (The capability has been advertised by the local router and received from the peer.) This feature was released with IOS 12.0. It allows policy changes to automatically be advertised to the peer without having to configure neighbor soft-reconfiguration .
8	Address family IPv4 Unicast: advertised and received	The local router and the peer are both running Multiprotocol BGP (MBGP). The peers have been activated to support unicast NLRI. See Chapter 7, "Large-Scale IP Multicast Routing," for a discussion of MBGP and address family indicators. As with the preceding line, the capability has been advertised to the peer and has been received from the peer.
9	Address family IPv4 Multicast: advertised and received	Both peers are activated to support MBGP multicast NLRI.
10	Received 7 messages, 0 notifications, 0 in queue	Seven BGP messages, including keepalives , have been received from this peer. No notification messages have been received, and no received messages are in the queue.
11	Sent 7 messages, 0 notifications, 0 in queue	Seven BGP messages, including keepalives, have been sent to this peer. No notification messages have been sent, and no messages to be sent are in the queue.
12	Route refresh request: received 0, sent 0	No route refresh requests (for the BGP Soft Reset Enhancement) have been received from or sent to this peer.
13	Minimum time between advertisement runs is 5 seconds	Update messages can be sent no closer than 5 seconds apart.
14	For address family: IPv4 Unicast	The indented lines beneath this line pertain to the unicast BGP routing table.
15	BGP table version 1, neighbor version 1	The neighbor has been updated with version 1 of the unicast BGP routing table, and the local router has been updated with version 1 of the peer's unicast BGP table.
16	Index 1, Offset 0, Mask 0x2	Internal indices to reference the specific peer. These fields have significance only to Cisco personnel who have access to the source code.
17	Pooh peer-group member	The neighbor is a member of the unicast peer group Pooh.
18	0 accepted prefixes consume 0 bytes	This line specifies how many unicast prefixes have been accepted from the peer and how many bytes of memory the prefixes have consumed. In this case, no prefixes have been received.
19	Prefix advertised 0, suppressed 0, withdrawn 0	No unicast prefixes have been advertised to, suppressed from, or withdrawn from this peer.
20	For address family: IPv4 Multicast	The indented lines beneath this line pertain to the multicast BGP routing table.
21	BGP table version 1, neighbor version 1	The neighbor has been updated with version 1 of the multicast BGP routing table, and the local router has been updated with version 1 of the peer's multicast BGP table.
22	Index 1, Offset 0, Mask 0x2	Internal indices to reference the specific peer. These fields have significance only to Cisco personnel who have access to the source code.
23	0 accepted prefixes consume 0 bytes	This line specifies how many multicast prefixes have been accepted from the peer and how many bytes of memory the prefixes have consumed. In this case, no prefixes have been received.
24	Prefix advertised 0, suppressed 0, withdrawn 0	No multicast prefixes have been advertised to, suppressed from, or withdrawn from this peer.
25	Connections established 1; dropped 0	A BGP connection and adjacency have been established with this peer only once, and no connection to this peer has ever been dropped.
26	Last reset 00:04:17, due to Address family activated	The last reset of the peer session occurred 4 minutes and 17 seconds ago, when MBGP was activated.
27	Connection state is ESTAB, I/O status: 1, unread input bytes: 0	Connection state is the state of the peer connection ” essentially , a repeat of the state shown on line 4. I/O status describes the internal status of the connection. Unread input bytes is the number of bytes not yet processed by BGP.
28	Local host: 10.100.1.2, Local port: 11012	This line is the local IP socket, consisting of the IP address and the local TCP port number.
29	Foreign host: 10.100.1.1, Foreign port: 179	This is the socket of the peer, consisting of the peer's IP address and TCP port. Comparing line 28 with this line, you can see that the local router initiated the TCP connection, because it uses an ephemeral port and connects to the well-known BGP port 179.
30	Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)	The number of packets waiting in a queue for retransmit, for input, or misordered packets.
31	Event Timers (current time is 0x3ABFA00):	This line is the header for the event timers that follow.
32	Timer, Starts, Wakeups, Next	The column headers for the event timers.
33	Retrans	Determines how long a transmitted frame can remain unacknowledged before the Cisco IOS Software polls for an acknowledgment.
34	TimeWait	Determines how long the local TCP connection waits to be sure that the remote TCP host has received the acknowledgment of its connection-termination request.
35	AckHold	Number of times the system failed to piggyback data required on a TCP acknowledgment. Such piggybacking can significantly reduce network traffic.
36	SendWnd	Timers for sending 0 window probes. Essentially, this field reflects how often users overload the remote host with data and how long it takes users to send it. For most normal Cisco IOS Software applications, this value should be 0.
37	KeepAlive	Determines the frequency (in seconds) at which the Cisco IOS Software sends messages to itself (Ethernet and Token Ring) or to the other end (serial) to ensure that a network interface is alive . The keepalive interface configuration command is used to set this timer.
41	iss: 2227710177 snduna: 2227710341 sndnxt: 2227710341 sndwnd: 16221	These are sequence numbers used by the TCP connection. iss = The initial send sequence number. snduna = The send unanswered sequence number; the last sequence number the local host sent but has not received an acknowledgment for. sndnxt = The sequence number the local router will send next. sndwnd = The TCP window size of the remote peer.
42	irs: 1632859231 rcvnxt: 1632859395 rcvwnd: 16221 delrcvwnd: 163	These sequence numbers apply to the remote side of the TCP connection. irs = The initial receive sequence number. rcvnxt = The last receive sequence number the local router has acknowledged . rcvwnd = The local router's TCP window size. delrcvwnd = Delayed receive window ”data the local host has read from the connection but has not yet subtracted from the receive window the host has advertised to the remote host. The value in this field gradually increases until it is larger than a full- sized packet, at which point it is applied to the rcvwnd field.
43	SRTT: 540 ms, RTTO: 3809 ms, RTV: 1364 ms, KRTT: 0 ms	These figures pertain to the latency of the connection between the peer. SRTT = The calculated smooth round-trip time. RTTO: The round-trip timeout. RTV = The variance of the round-trip time. KRTT = The Karn round-trip time; new round-trip timeout (using the Karn algorithm). This field separately tracks the round-trip time of packets that have been retransmitted.
44	minRTT: 8 ms, maxRTT: 300 ms, ACK hold: 200 ms	These values are a continuation of the performance values begun on line 43. minRTT = The smallest recorded round-trip time. maxRTT = The largest recorded round-trip time. ACK hold = The time the local router will delay an acknowledgment so that it can piggyback data onto it.
45	Flags: higher precedence, nagle	IP precedence of the BGP packets.
46	Datagrams (max data segment is 536 bytes):	This is the header for the next two lines, which provide statistics about BGP Updates sent to and received from the peer. It also shows that the maximum TCP segment size is 536 bytes.
47	Rcvd: 11 (out of order: 0), with data: 7, total data bytes: 163	Statistics on received updates, including total received, datagrams with data, and total bytes.
48	Sent: 14 (retransmit: 0), with data: 7, total data bytes: 163	Statistics of BGP updates sent to the peer, including total sent, number of updates containing data, and total bytes.