Month: March 2025

I was reading an article about ECMP (Equal Cost Multipath) for traffic load sharing, and it brought back memories of my previous traffic engineering tests. It seems simple at first glance, but it’s actually more complex—especially when it comes to policy-based routing.

The challenge lies in determining traffic redirection and sharing in a session-wise connection, whether with or without NAT, across multiple links or circuits with different latencies. There’s also the complication of firewall interception with asymmetric return traffic. These factors make achieving ideal traffic load sharing quite difficult.

Of course, if tunneling is involved, things get simpler. It essentially blinds both endpoints and allows you to add two routes with the same metric in overlay routing. However, it doesn’t clearly explain why load-sharing performance behaves the way it does.

What about service enhancement? If the primary link becomes congested, should the secondary link pick up some of the traffic? That’s not exactly round-robin behavior—it would require active measurement and monitoring of the links. Maintaining session flow on the primary link while redirecting new flows to the secondary link sounds ideal, but it’s difficult to implement. For MPLS-TE, that’s straightforward—but what if you have two internet links, like one DIA (Direct Internet Access) and one mobile network? How would you handle that?

Well, just for fun, I haven’t done any serious measurements yet. But after setting up load sharing on my node, it seems to be working—though I haven’t really thought through the next steps. Running a Speedtest shows that the flows (by ports) are transmitting separately. Hmm… not ideal, but not bad either. But what about other applications? If they’re using two different IP addresses for outgoing traffic—ahhhh…

Let’s discuss this, bro.

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Enable 2 Multipath load sharing
sudo ip route add default scope global \
nexthop via 192.168.X.X dev XXX weight 1 \
nexthop via 192.168.X.X dev XXX weight 1

For multipath routing, disabling connection tracking for locally-generated traffic helps
sudo sysctl -w net.netfilter.nf_conntrack_tcp_loose=0

Enable Layer 4 Hashing
sudo sysctl -w net.ipv4.fib_multipath_hash_policy=1

Enable IP Forwarding
sudo sysctl -w net.ipv4.ip_forward=1

Force More Aggressive Flow-Based Balancing:
Set rp_filter to 0 (disable reverse path filtering) so the kernel won’t drop asymmetric traffic
sudo sysctl -w net.ipv4.conf.all.rp_filter=0

Flush all route cache
sudo ip route flush cache

#ECMP #Linux #Internet #Routing #IP #Firewall #Tunneling #MPLS #trafficEngineering #ChatGPT