Sunday, August 2, 2020

ERSPAN decapsulation on Linux

Wondering if anyone has gotten this to work. I'm using Security Onion and have a CentOS7 VM as my sensor. I have ERSPAN configured in VMWare (Type II or Type III) on the VDS to traffic to the Linux sensor node's monitor NIC IP. This is working - I can see the ERSPAN traffic coming in:

18:21:46.442220 IP esxihost.internal > hunter-sensor: GREv0, seq 205937, length 161: gre-proto-0x22eb

Per this site, I enabled IP_GRE, set up the monitoring interface, etc, but it doesn't seem to work. I never get traffic on mon0. https://brezular.com/2015/05/03/decapsulation-erspan-traffic-with-open-source-tools/

ip a show mon0 gives me

219: mon0@NONE: <NOARP,UP,LOWER\_UP> mtu 1476 qdisc noqueue state UNKNOWN group default qlen 1000

link/gre 10.85.167.40 brd 0.0.0.0

inet 1.1.1.1/30 scope global mon0

valid_lft forever preferred_lft forever

I've tried this a million times, redoing it, always doesn't work.

It doesn't seem like it should be difficult to decapsulate ERSPAN traffic.

Any thoughts or help would be GREATLY!!! appreciated.



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