For JUNOS I think that you are looking for user@lab> show forwarding-options load-balance ? Possible completions: destination-address Destination IP address destination-port Destination port family Layer 3 family ingress-interface Ingress Logical Interface packet-dump Raw packet dump in hex without '0x' source-address Source IP address source-port Source port tos Type of Service field transport-protocol Transport layer protocol Nitzan On Tue, Aug 12, 2025 at 5:58 PM Saku Ytti via NANOG <nanog@lists.nanog.org> wrote:
Hey-o,
Which platform/software has a command to show which interface will be used for forwarding with given keys?
ASR9k has a cef exec-route, and I see references to this in c-nsp, reddit and cisco.com forums, stressing how useful debugging tool it has been. Despite it not actually working, since it's just RE software, it doesn't talk to the EZchip/lightspeed, unless it has been fixed in the past couple of years, certainly hasn't worked in the timeline of various forums finding it useful.
MX has 'jsim' https://www.juniper.net/documentation/en_US/day-one-books/TW_MX3D_PacketWalk... which I think actually works, but it is quite involved. I have some (false?) memory that I saw in some release note this being a bit more productised into CLI command, but I'm failing to find anything to support this memory.
There is also RFC5837, which is actually implemented in QFX5k, but not for TTL exceeded, we've opened ER to get it supported on MX and PTX and for TTL exceeded. This RFC will allow programmatic platform agnostic discovery of the actual interface used, without relying on platform specific magic. So please do ask your vendors to implement it.
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