R3102-R3103-HP 6600/HSR6600 Routers Layer 3 - IP Routing Configuration Guide

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Enabling BGP and IGP route synchronization
Routing information synchronization between IBGP and IGP avoids giving wrong directions to routers
outside of the local AS.
By default, upon receiving an IBGP route, a BGP router checks the route's next hop. If the next hop is
reachable, the BGP router advertises the route to EBGP peers. If a non-BGP router works in an AS, it can
discard a packet due to an unreachable destination. As shown in Figure 68, R
outer E has learned a route
of 8.0.0.0/8 from Router D through BGP. Router E then sends a packet to 8.0.0.0/8 through Router D,
which finds from its routing table that Router B is the next hop (configured using the peer next-hop-local
command). Because Router D has learned the route to Router B through IGP, Router D forwards the
packet to Router C through route recursion. Router C does not know the route 8.0.0.0/8, so it discards
the packet.
Figure 68 IBGP and IGP synchronization
For this example, if synchronization is enabled, and the route 8.0.0.0/24 received from Router B is
available in its IGP routing table, Router D advertises the IBGP route when the following conditions are
met:
• The next hop of the route is reachable.
• An active route with the same destination network segment is available in the IGP routing table (use
the display ip routing-table protocol command to check the IGP route state).
You can disable the synchronization feature in the following situations:
• The local AS is not a transitive AS (AS 20 is a transitive AS in the above figure).
• Routers in the local AS are IBGP fully meshed.
To enable BGP and IGP synchronization:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enter BGP view.
bgp as-number N/A
3. Enable synchronization
between BGP and IGP.
synchronization Not enabled by default.
Limiting prefixes received from a peer or peer group
This feature can prevent that send a large number of BGP routes to the router.