[lvs-users] IPVS uses loopback address for tunneling outer source IP

To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: [lvs-users] IPVS uses loopback address for tunneling outer source IP
From: Yunzhao li <yzli.ksu@xxxxxxxxx>
Date: Wed, 29 Aug 2018 10:53:00 -0700

We are seeing some very strange thing on IPVS tunnel mode(we are
running centos 7 with kernel 3.10.0):

Occasionally, the tcpdump shows that IPVS changes tunnelled outer
source IP address to a loopback address, like, and the
tunnelled packets had been dropped . However, most of time, the outer
source IP address is the normal IP address bind to the physical
ethernet interface. When this happened, we dumped the routing tables
and iptables, and it looks this issue is not due to either routing
setting or a iptables' SNAT. Since this issue happened on two hosts,
we also doubt that this is a hardware problem. We also briefly checked
the ip_vs_tunnel_xmit() call and it looks it retrieves outer header
information from kernel's routing part. We are wondering whether this
is a desired behaviour of IPVS, due to IPVS doesn't want to send out
packets at that time?



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