Developers Guide

When a BGP neighbor connection with authentication configured is rejected by a passive peer-group, Dell EMC Networking OS
does not allow another passive peer-group on the same subnet to connect with the BGP neighbor. To work around this, change
the BGP configuration or change the order of the peer group configuration.
You can constrain the number of passive sessions accepted by the neighbor. The limit keyword allows you to set the total
number of sessions the neighbor will accept, between 2 and 265. The default is 256 sessions.
1. Configure a peer group that does not initiate TCP connections with other peers.
CONFIG-ROUTER-BGP mode
neighbor peer-group-name peer-group passive limit
Enter the limit keyword to restrict the number of sessions accepted.
2. Assign a subnet to the peer group.
CONFIG-ROUTER-BGP mode
neighbor peer-group-name subnet subnet-number mask
The peer group responds to OPEN messages sent on this subnet.
3. Enable the peer group.
CONFIG-ROUTER-BGP mode
neighbor peer-group-name no shutdown
4. Create and specify a remote peer for BGP neighbor.
CONFIG-ROUTER-BGP mode
neighbor peer-group-name remote-as as-number
Only after the peer group responds to an OPEN message sent on the subnet does its BGP state change to ESTABLISHED. After
the peer group is ESTABLISHED, the peer group is the same as any other peer group.
For more information about peer groups, refer to Configure Peer Groups.
Enabling Graceful Restart
Use this feature to lessen the negative effects of a BGP restart.
Dell EMC Networking OS advertises support for this feature to BGP neighbors through a capability advertisement. You can
enable graceful restart by router and/or by peer or peer group.
NOTE: By default, BGP graceful restart is disabled.
The default role for BGP is as a receiving or restarting peer. If you enable BGP, when a peer that supports graceful restart
resumes operating, Dell EMC Networking OS performs the following tasks:
● Continues saving routes received from the peer if the peer advertised it had graceful restart capability. Continues forwarding
traffic to the peer.
● Flags routes from the peer as Stale and sets a timer to delete them if the peer does not perform a graceful restart.
● Deletes all routes from the peer if forwarding state information is not saved.
● Speeds convergence by advertising a special update packet known as an end-of-RIB marker. This marker indicates the peer
has been updated with all routes in the local RIB.
If you configure your system to do so, Dell EMC Networking OS can perform the following actions during a hot failover:
● Save all forwarding information base (FIB) and content addressable memory (CAM) entries on the line card and continue
forwarding traffic while the secondary route processor module (RPM) is coming online.
● Advertise to all BGP neighbors and peer-groups that the forwarding state of all routes has been saved. This prompts all
peers to continue saving the routes they receive and to continue forwarding traffic.
● Bring the secondary RPM online as the primary and re-open sessions with all peers operating in No Shutdown mode.
● Defer best path selection for a certain amount of time. This helps optimize path selection and results in fewer updates being
sent out.
To enable graceful restart, use the following command.
bgp graceful-restart [restart-time seconds] [stale-path-time seconds] [role receiver-only]
To return to the default, use the no bgp graceful-restart command.
● Enable graceful restart for the BGP node.
CONFIG-ROUTER-BGP mode
202
Border Gateway Protocol (BGP)