ā12-04-2021 04:32 AM
Dear Gents
Why should Enable Cef if we need to perform BGP multipath , what if it is not enabled and router is working on Fast or process switching, what issue may cause ,
future more
can we apply BGP Load Balancing per Packet , or per destination , ( inbound and outbound )
only Scenario I am sure about it is load sharing ( per subnet )
ā12-04-2021 05:59 AM
Load balancing over the multipaths is performed by CEF. CEF load balancing is configured on a per-packet round robin or on a per session (source and destination pair) basis.
below guide help more understanding :
https://www.cisco.com/c/en/us/td/docs/ios/12_2sx/feature/guide/fsxeibmp.html
ā12-04-2021 06:36 AM
"Why should Enable Cef if we need to perform BGP multipath , what if it is not enabled and router is working on Fast or process switching, what issue may cause ,"
What might be caused, and likely will, without CEF enabled, is much slower packet routing, especially of the first packet of a flow. It might also increase the work load on the device.
"can we apply BGP Load Balancing per Packet , or per destination , ( inbound and outbound )
only Scenario I am sure about it is load sharing ( per subnet ) "
First, load balancing would be outbound, not inbound. Second, (as already noted by @balaji.bandi), CEF load balancing is per packet, per flow, which often tends to very nicely/well balance egress link loads. However, although in theory, IP doesn't guarantee flow packet sequence, which TCP does, many applications not using TCP are "disturbed" by flow packet re-sequencing, and even TCP, may initially consider packets arriving out of sequence as having been "lost" in transit, which may invoke TCP's flow rate back-off and/or retransmission of "lost" packets. So, avoiding packet by packet LB is generally highly recommended!
ā12-04-2021 06:49 AM
many thanks
@balaji.bandi many thanks
@Joseph W. Doherty so If the router ( assuming ) is not using CEF we can do Load-sharing for BGP , right ?
and as you told me we can't guarantee traffic inbound so can we use per destination or it will be same issue
so we can only rely on per subnet ?
ā12-04-2021 12:12 PM
CEF did (not sure about all current implementations) allow/support per-packet LB. Otherwise, it's per flow, although don't recall if it LBs flows, to same prefix.
ā12-04-2021 10:54 AM
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide