Managing Routing Policy Changes - Cisco IE-4000 Software Configuration Manual

Configuring IP Unicast Routing
Configuring BGP
Received 2828 messages, 0 notifications, 0 in queue
Sent 2826 messages, 0 notifications, 0 in queue
Connections established 11; dropped 10
Anything other than state = established means that the peers are not running. The remote router ID is the highest IP
address on that router (or the highest loopback interface). Each time the table is updated with new information, the table
version number increments. A table version number that continually increments means that a route is flapping, causing
continual routing updates.
For exterior protocols, a reference to an IP network from the network router configuration command controls only which
networks are advertised. This is in contrast to Interior Gateway Protocols (IGPs), such as EIGRP, which also use the
network command to specify where to send updates.

Managing Routing Policy Changes

Routing policies for a peer include all the configurations that might affect inbound or outbound routing table updates.
When you have defined two routers as BGP neighbors, they form a BGP connection and exchange routing information.
If you later change a BGP filter, weight, distance, version, or timer, or make a similar configuration change, you must reset
the BGP sessions so that the configuration changes take effect.
There are two types of reset: hard reset and soft reset. The switch supports a soft reset without any prior configuration
when both BGP peers support the soft route refresh capability, which is advertised in the OPEN message sent when the
peers establish a TCP session. A soft reset allows the dynamic exchange of route refresh requests and routing
information between BGP routers and the subsequent re-advertisement of the respective outbound routing table.

When soft reset generates inbound updates from a neighbor, it is called dynamic inbound soft reset.

When soft reset sends a set of updates to a neighbor, it is called outbound soft reset.
A soft inbound reset causes the new inbound policy to take effect. A soft outbound reset causes the new local outbound
policy to take effect without resetting the BGP session. As a new set of updates is sent during outbound policy reset, a
new inbound policy can also take effect.
Table 64 Advantages and Disadvantages of Hard and Soft Resets
Type of Reset
Hard reset
Outbound soft reset
Dynamic inbound soft
reset
BEFORE YOU BEGIN
Enable BGP routing as described in the
Advantages
No memory overhead.
No configuration; no storing of routing table
updates.
Does not clear the BGP session and cache.
Does not require storing of routing table
updates and has no memory overhead.
Enabling BGP Routing, page
Disadvantages
The prefixes in the BGP, IP, and FIB tables
provided by the neighbor are lost. Not
recommended.
Does not reset inbound routing table updates.
Both BGP routers must support the route
refresh capability.
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