Information Technology Reference
In-Depth Information
On the other hand, messages accumulated in the output queue (OutQ) are moved by the
BGP I/O to the TCP socket.
The BGP Router process is a main BGP process that is responsible for initiating other BGP
processes, maintaining BGP sessions with neighbors, processing incoming updates from
peers and locally sourced networks, updating the IP RIB with BGP entries, and sending
updates to peers. Specifically, the BGP Router process receives commands entered from
Common Line Interface (CLI) via the parser. It interacts with the BGP I/O process for
update processing (sending and receiving) using per-neighbor queues, as shown in
Example 2-1. After all valid paths are installed into the BGP RIB, the BGP Router runs the
path selection and installs the best paths into the IP RIB. Events happening in the IP RIB
and the BGP RIB can also trigger appropriate actions in the BGP Router process. For
example, when a route needs to be redistributed from another protocol to BGP, IP RIB
notifies the BGP Router to update the BGP RIB.
BGP Queues
Example 2-1
router#show ip bgp summary
BGP router identifier 192.168.100.6, local AS number 100
BGP table version is 8, main routing table version 8
4 network entries and 7 paths using 668 bytes of memory
3 BGP path attribute entries using 180 bytes of memory
6 BGP rrinfo entries using 144 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP activity 4/74 prefixes, 11/4 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.100.4 4 100 1120 1119 8 0 0 17:12:34 3
192.168.100.5 4 100 1114 1111 8 0 0 00:07:35 3
InQ OutQ
The primary function of the BGP Scanner process is BGP housekeeping. Specifically,
the BGP Scanner performs periodic scans of the BGP RIB to determine if prefixes and
attributes should be deleted and if route map or filter caches should be flushed. This process
also scans the IP RIB to ensure that all the BGP next hops are still valid. If the next hop is
unreachable, all BGP entries using that next hop are removed from the BGP RIB. BGP
dampening information is also updated in each cycle. General scanning is performed every
60 seconds. BGP Scanner also accepts commands from CLI via the parser to change its
scan time.
Example 2-2 is a snapshot of the BGP processes and memory use in a Cisco 12000 router.
The Allocated column shows the total number of bytes allocated since the creation of the
process. The Freed column provides the number of bytes the process has freed since its
creation. The Holding column shows the actual memory that is being consumed by the
process at the moment. In this example, the BGP router process holds more than 34 MB
of memory, whereas BGP I/O and BGP Scanner hold 6 KB each.
