On 2/3/2023 4:54 AM, Michael Richardson via Bloat wrote:
A new network namespace would certainly work, but it may be unmanageable
overkill.
What you probably need are policy-based routes, which you can establish
statically and then --source ought to work.
That's exactly what turned out to be the issue. I'd already planned to
implement it to make some clients use the alternate ISP, but didn't
realize it applies to packets with source address set to that interface.
I'd read through a few tutorials and tested that and it worked!
I put these into "up" statements into my /etc/network/interfaes, but you say
you are running RHEL... I'm sure that there is a netplan way.
This also means that if you have a monitoring system elsewhere (smokeping or
something), and you ping each interface, then it will reply on that
interface.
That turned out to be harder to figure out. RHEL 8 is a transition from
traditional network scripts in /etc/sysconfig/network-scripts to
NetworkManager connections. So the RH NM has to be able to understand
the old files. I'm used to editing files with a text editor to make
changes, but the RHEL docs don't expose the NM files and require one to
use a manager program (nmcli) to make changes. I have no idea where my
rules went when I changed them with nmcli. I do see the new
per-interface route tables in the old scripts location. RHEL 9 moves
over completely to NM, so I'll need to figure out how to migrate the
config when I upgrade.
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_and_managing_networking/configuring-policy-based-routing-to-define-alternative-routes_configuring-and-managing-networking
BTW, I noticed that the numeric routing table IDs are 32-bit, but the
reserved IDs are from 0-255. Some online tutorials specify that custom
tables need to be in the 8-bit range. I suspect that the earliest
implementation used a single byte for the table ID and it widened in
later kernels. The example number used in the above documentation is
5000. So I'm using 2000 and 4000 for eno2 and eno4. (eno3 is the default
link and eno1 is the LAN with an explicit global rule.)
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