BGP TCP Tuning
Introduction
BGP runs on top of TCP just like any other application. Tuning the TCP parameters can significantly decrease the initial convergence time of synchronizing the BGP table.
TCP MSS
- The TCP MSS is the maximum segment size that can be sent in an IP packet. The closer the MSS is to the MTU the more efficient is the transfer of BGP messages.
- Each direction of data flow can use a different MSS value.
PMTUD
- Path MTU Discovery is a mechanism to find the end to end MTU.
- Using jumbo frame can cut down on the number of BGP messages sent and the number of TCP ACK received.
- One issue could occur using iBGP or multi-hop eBGP where a backup path for the BGP TCP session has a smaller MTU than the primary path. Already established BGP sessions might be fragmented and cause performance issue for further large synchronization.