Ulog/filter device name does not match effective device name of data flow: expected?

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Hi,

Just a question, if this is intended behavior in NAT/logging with ulog/filter, I know it should be some border case:


In test environment, all 10/8 IPs are routed via lo by default to avoid test data from 10/8 net leaving the host.

10.0.0.0/8 dev lo  scope link  src 10.0.0.1

To allow some connections to reach machines outside, these connections are natted, e.g.

Iptables -t nat -A OUTPUT -o lo -d 10.0.0.5 -p tcp -m tcp --dport 80 -j DNAT --to-destination xxx.172:80

This allows to create the connection, but with two side effects:

Although the package leaves via eth0, ulog will report OUT=lo:

Jan 10 12:06:13 v3lsn1105 iptables:ACCEPT-INFO IN= OUT=lo MAC= SRC=10.xx.xx.3 DST=xxxx.172 LEN=60 TOS=00 PREC=0x00 TTL=64 ID=46425 CE DF PROTO=TCP SPT=48808 DPT=80 SEQ=1237479374 ACK=0 WINDOW=32792 SYN URGP=0

To accept the connection, OUTPUT on lo has to be accepted (using filter rule with -o lo), although package leaves via eth0.

Is this expected behavior?

Kind regards,
Roman

DI Roman Fiedler
Engineer
Safety & Security Department
Information Management & eHealth

AIT Austrian Institute of Technology GmbH
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