Table of Contents
How can we reduce convergence time in BGP?
You can activate best-external advertisement on the backup leaf to minimize the convergence process and the resulting convergence times. This feature enables the advertisement of best external BGP routes to internal BGP peers, even when the external BGP route is not the best path.
How long does it take for BGP to converge?
This takes up to 60 seconds depending on the when the BGP Scanner process last ran. So even with a super optimized IGP, BGP will be very slow to converge.
What is BGP fast reroute?
When a link fails, the packets on the link are discarded, and a routing loop might occur until BGP completes routing convergence based on the new network topology. You can enable BGP fast reroute (FRR) to resolve this issue. When the link to Router D fails, BGP directs packets to the backup next hop.
Why is BGP slow protocol?
Routing changes on the Internet occur all the time. If BGP had to react to every change, it would flood the Internet with routing updates that could slow traffic all over the globe. So, BGP plays a waiting game to give routes time to settle down. This is why BGP is seldom used as an internal routing protocol.
How long does BGP failover take?
The failover time for the default i-BGP peering session with the default value of the waiting interval is 5 seconds. The failure time on the primary link does not affect the secondary link and tertiary link.
What is convergence in BGP?
All Interior Gateway Protocols rely on convergence to function properly. To have converged it is the normal state of an operational autonomous system. The Exterior Gateway Routing Protocol BGP typically never converges because the Internet is too big for changes to be communicated fast enough.
How often does BGP update routes?
BGP neighbors, called peers, are established by manual configuration among routers to create a TCP session on port 179. A BGP speaker sends 19-byte keep-alive messages every 30 seconds (protocol default value, tunable) to maintain the connection.
Which ones are types of fast reroute?
In this post you will see the following mechanism for fast reroute, pros and cons of each one of them and applications of these mechanisms.
- Loop Free Alternates (RFC5286, deployable today)
- Remote Loop Free Alternates (draft in RTGWG, implemented by some vendors)
- MRT-FRR (draft in RTGWG, proto-types in progress)
How many ECMP paths are advertised by default?
A vSmart will advertise 4 ECMP paths by default, maximum is 16.
How often are BGP updates sent?
To maintain the most stable routing table, BGP introduced a minimum delay between updates for a neighbor session. This interval is called Advertisement Interval. On Cisco routers, the default advertisement interval is 30 seconds for eBGP peers and 0 seconds for iBGP peers.
What is fast convergence?
Convergence time is a measure of how fast a group of routers reach the state of convergence. It is one of the main design goals and an important performance indicator for routing protocols, which should implement a mechanism that allows all routers running the protocol to quickly and reliably converge.
What is BGP hold time?
The hold time is three times the interval at which keepalive messages are sent. BGP on the local routing device uses the smaller of either the local hold-time value or the peer’s hold-time value received in the open message as the hold time for the BGP connection between the two peers.