Possible unexpected behavior routing from single interface to multiple interfaces

[jhamlin96]

Hello,

I am possibly seeing unexpected behavior with routing from one interface to multiple other interfaces. I observe that a packet from elsewhere to eth0 with TTL 6 is received, and routed to eth1, and TTL is decremented by 1 as expected. When this same packet is also routed from eth0 to eth2, I would expect the TTL to also be 5 since it has only crossed a single hop, but it is 4.

[troglobit]

Hi!

You need to tell us more about your setup. Show us the configuration file and tell us what version you are using. As well as what operating system you are running on. Smcroute runs on many different flavours of Unix.

Thanks /Joachim

[jhamlin96]

Joachim, Sorry for not providing this information initially - I was half expecting you to correct my interpretation of the routing specification.

I am running on a Redhat 7.9 host, smcroute 2.5.3. I am not using any configuration file, instead running the smcroutectl commands: smcroutectl join eth0 239.255.0.1 smcroutectl add eth0 239.255.0.1 eth1 smcroutectl add eth0 239.255.0.1 eth2

Happy to provide more info or help test and debug.

[troglobit]

That's a very simple use-case, that should work fine with the latest version of SMCRoute. Hmm, what kernel version is this? And could you provide the output of both

- /proc/net/ip_mr_vif
- /proc/net/ip_mr_cache

I just tested the same setup with CORE, and it works fine on Linux 5.11 (Linux Mint 20.2). I inject frames with TTL 6 and get TTL 5 on both my output interfaces.

Do you perhaps have some firewall/NAT rules configured? I'm completely useless with iptables/nftables, but this sounds like it could be caused by something like that, unless it's a kernel bug.

[troglobit]

Closing due to inactivity, also, very likely not an SMCRoute problem.