BGP multipath limit

[zdmr]

Hi there,

I see a statement in the following document on page 2: "The valid values for the maximum-paths command range from 1 to 32. However, the maximum value that can be configured is 2."

Document link: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/17-1/configuration_guide/mpls/b_171_mpls_9500_cg/configuring_eibgp___multipath.pdf

What does it mean? How many paths (ISPs) can eBGP use at the same time — 2 or more? Do not consider device, MPLS-VPN etc.

Thanks in advance.

[stephan.l.martin1]

The multipath option is just as you suspect but can be applied to both eBGP or iBGP. The limitation is platform specific. The essence of multipath is that it allows you to perform load-balancing utilizing CEF. The standard behavior is to only install the BEST route. This feature allows you to override that and install a second route for load-balancing purposes.

HTH!

[MHM Cisco World]

Ios xe is run on 

C9000 series 

Asr 1k 

So max path can config from 1 to 32 

For this particular platform c9500 the max path is 2.

So it platform limitations 

MHM

[M02@rt37]

Hello @zdmr 

The statement in the document refers to the configuration constraints for the maximum-paths command in the context of eBGP multipath on Catalyst 9500 switches. 

The maximum-paths command supports values ranging from 1 to 32, meaning you can theoretically configure eBGP to load-balance traffic across up to 32 paths. The document states that only 2 paths can actually be utilized at the same time for eBGP multipath load balancing on these devices. This is a hardware or platform limitation, restricting eBGP multipath to a maximum of 2 paths regardless of the broader range allowed by the command syntax.

How Many ISPs Can eBGP Use Simultaneously? For a C9500 switch, the eBGP multipath feature allows load balancing across only 2 ISPs (or 2 eBGP paths) at the same time.