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Some packets flagged INVALID

DISCUSSION Bob Sauvage 3 participants 3 messages Feb 18, 2014

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Bob Sauvage

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#0 lore raw

Hi *,

I'm running a high volume web application that uses Apache 2.2.15 mod_proxy to reverse proxy content from apache to JBoss 6.

I found 503 errors which happen sporadically throughout the day on random requests (perhaps 1/1000 of daily requests).

After investigations, I noticed that every error coincides with an invalid tcp packet:

kernel: invalid:IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=33082 DF PROTO=TCP SPT=48340 DPT=8080 WINDOW=32792 RES=0x00 SYN URGP=0

After some investigations, this SYN packet is not acknowledged by JBoss in order to perform the TCP 3-Way Handshake. Mhmm, strange, I decide to investigate in firewall rules, build by another sysadmin:

In the INPUT chain, I found a rule that logs and REJECTS all INVALID packets:

iptables -A INPUT -m state --state INVALID -j LOG --log-prefix "invalid:" iptables -A INPUT -m state --state INVALID -j REJECT

Then logs and REJECTS not SYN but new:

iptables -A INPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "new-not-syn:" iptables -A INPUT -p tcp ! --syn -m state --state NEW -j REJECT --reject-with tcp-reset

I decided to add a rule in order to ACCEPT all packets from 127.0.0.1 to or from port 8080.

Since this update, I don't see this kind of errors anymore.

Why does iptables tag this packet as invalid ?

Thanks,

Bob

#1 lore raw
Quoted 32 lines · Bob Sauvage

Hi *,

I'm running a high volume web application that uses Apache 2.2.15 mod_proxy to reverse proxy content from apache to JBoss 6.

I found 503 errors which happen sporadically throughout the day on random requests (perhaps 1/1000 of daily requests).

After investigations, I noticed that every error coincides with an invalid tcp packet:

kernel: invalid:IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=33082 DF PROTO=TCP SPT=48340 DPT=8080 WINDOW=32792 RES=0x00 SYN URGP=0

After some investigations, this SYN packet is not acknowledged by JBoss in order to perform the TCP 3-Way Handshake. Mhmm, strange, I decide to investigate in firewall rules, build by another sysadmin:

In the INPUT chain, I found a rule that logs and REJECTS all INVALID packets:

iptables -A INPUT -m state --state INVALID -j LOG --log-prefix "invalid:" iptables -A INPUT -m state --state INVALID -j REJECT

Then logs and REJECTS not SYN but new:

iptables -A INPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "new-not-syn:"
iptables -A INPUT -p tcp ! --syn -m state --state NEW -j REJECT --reject-with tcp-reset

Quoted 6 lines

I decided to add a rule in order to ACCEPT all packets from 127.0.0.1 to or from port 8080.

Since this update, I don't see this kind of errors anymore.

Why does iptables tag this packet as invalid ?

I believe INVALID applies to all packets that netfilter has no clue why it has receieved them. Often, it's a RST or FIN for a non-existent conn or one recently torn-down. DDoS packets are often INVALID.

I think those 'syn' rules above are 'defective' (or extraneous). For TCP, only a SYN packet should be tagged NEW because there is no other way to initiate a TCP conn.

In this particular case, it may be that the SYN arrived during the grace period after a previous matching conn was torn down. (Related to SO_REUSEADDR?)

#2 lore raw
Quoted 40 lines · Neal Murphy
Quoted 32 lines · Bob Sauvage

Hi *,

I'm running a high volume web application that uses Apache 2.2.15 mod_proxy to reverse proxy content from apache to JBoss 6.

I found 503 errors which happen sporadically throughout the day on random requests (perhaps 1/1000 of daily requests).

After investigations, I noticed that every error coincides with an invalid tcp packet:

kernel: invalid:IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=33082 DF PROTO=TCP SPT=48340 DPT=8080 WINDOW=32792 RES=0x00 SYN URGP=0

After some investigations, this SYN packet is not acknowledged by JBoss in order to perform the TCP 3-Way Handshake. Mhmm, strange, I decide to investigate in firewall rules, build by another sysadmin:

In the INPUT chain, I found a rule that logs and REJECTS all INVALID packets:

iptables -A INPUT -m state --state INVALID -j LOG --log-prefix "invalid:" iptables -A INPUT -m state --state INVALID -j REJECT

Then logs and REJECTS not SYN but new:

iptables -A INPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "new-not-syn:"
iptables -A INPUT -p tcp ! --syn -m state --state NEW -j REJECT --reject-with tcp-reset

Quoted 6 lines

I decided to add a rule in order to ACCEPT all packets from 127.0.0.1 to or from port 8080.

Since this update, I don't see this kind of errors anymore.

Why does iptables tag this packet as invalid ?

Quoted 7 lines

I believe INVALID applies to all packets that netfilter has no clue why it has receieved them. Often, it's a RST or FIN for a non-existent conn or one recently torn-down. DDoS packets are often INVALID.

I think those 'syn' rules above are 'defective' (or extraneous). For TCP, only a SYN packet should be tagged NEW because there is no other way to initiate a TCP conn.

right, but in a fail-over scenario with conntrackd you need to set a sysctl to allow:

nf_conntrack_tcp_loose - BOOLEAN
0 - disabled
not 0 - enabled (default)

If it is set to zero, we disable picking up already established connections.

or you might tune the behaviour with:

nf_conntrack_tcp_be_liberal - BOOLEAN
0 - disabled (default)
not 0 - enabled

Be conservative in what you do, be liberal in what you accept
from others.
If it's non-zero, we mark only out of window RST segments as
INVALID.

see:
Documentation/networking/nf_conntrack-sysctl.txt

in your kernel source dir.

Quoted 4 lines

In this particular case, it may be that the SYN arrived during the grace period after a previous matching conn was torn down. (Related to SO_REUSEADDR?)