Dell BigIron RX Series, Configuration Manual

Page: 820 / 1458

744 BigIron RX Series Configuration Guide
53-1002253-01
Brocade implementation of BGP4
26
BGP4 Router A sends a Hold Time of 5 seconds and BGP4 Router B sends a Hold Time of 4
seconds, both routers use 4 seconds as the Hold Time for their BGP4 session. The default Hold
Time is 180 seconds. Generally, the Hold Time is configured to three times the value of the Keep
Alive Time.
If the Hold Time is 0, a BGP4 router assumes that its neighbor is alive regardless of how many
seconds pass between receipt of UPDATE or KEEPALIVE messages.
NOTIFICATION message
When you close the router’s BGP4 session with a neighbor, or the router detects an error in a
message received from the neighbor, or an error occurs on the router, the router sends a
NOTIFICATION message to the neighbor. No further communication takes place between the BGP4
router that sent the NOTIFICATION and the neighbors that received the NOTIFICATION.
REFRESH message
BGP sends a REFRESH message to a neighbor to request the neighbor to resend route updates.
This type of message can be useful if an inbound route filtering policy has been changed.
Brocade implementation of BGP4
BGP4 is described in RFC 1771 and the latest BGP drafts. The Brocade implementation fully
complies with RFC 1771 and also supports the following:
•
RFC 1745 (OSPF Interactions)
•
RFC 1997 (BGP Communities Attributes)
•
RFC 2385 (TCP MD5 Signature Option)
•
RFC 2439 (Route Flap Dampening)
•
RFC 2796 (Route Reflection)
•
RFC 2842 and 3392 (Capability Advertisement)
•
RFC 3065 (BGP4 Confederations)
•
RFC 2858 (Multiprotocol Extensions)
•
RFC 2918 (Route Refresh Capability)
•
RFC 3392 (BGP Capability Advertisement)
Memory considerations
BGP4 handles a very large number of routes and therefore requires a lot of memory. For example,
in a typical configuration with just a single BGP4 neighbor, a BGP4 router may need to be able to
hold up to 150,000 routes. Many configurations, especially those involving more than one
neighbor, can require the router to hold even more routes. The device provide dynamic memory
allocation for BGP4 data. These devices automatically allocate memory when needed to support
BGP4 neighbors, routes, and route attribute entries. Dynamic memory allocation is performed
automatically by the software and does not require a reload.