Iptables command ignored without error message

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Valchris
DD-WRT Novice


Joined: 28 Aug 2020
Posts: 2

PostPosted: Fri Aug 28, 2020 22:51    Post subject: Iptables command ignored without error message Reply with quote
Hello, I am running an iptables command from telnet to my router, each time I run the command it seems to have no effect and I can't see it listed in the list of rules.

Code:
root@DD-WRT:~# iptables -t mangle -I POSTROUTING -o `get_wanface` -j TTL --ttl-set 65 -v


Returns the following output:
Code:
TTL  0 opt -- in * out vlan2  0.0.0.0/0  -> 0.0.0.0/0  TTL set to 65


As far as I can tell, this looks correct. So I tried to check the tables to ensure the rule is listed:

Code:
root@DD-WRT:~# iptables -t mangle -vnL POSTROUTING


And the response I get appears to be blank:

Code:
Chain POSTROUTING (policy ACCEPT 108K packets, 60M bytes)                                                                                                                                    pkts bytes target     prot opt in     out     source               destination 


Please help me understand where I am going wrong.


Relevant router specs:
    DD-WRT v3.0-r42729 std (c) 2020 NewMedia-NET GmbH
    Release: 03/18/20
    Board: TP-Link ARCHER-A7 v5
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eibgrad
DD-WRT Guru


Joined: 18 Sep 2010
Posts: 8343

PostPosted: Sat Aug 29, 2020 0:03    Post subject: Reply with quote
On dd-wrt, the fact it reports adding the rule doesn't necessarily mean it did (yeah, weird). For space saving reasons, dd-wrt removes many error messages from the system (these days, w/ the amount of flash typically available, that shouldn't be necessary, but given the continued need to support legacy routers, it just is).

If I run that command on tomato (which I know doesn't support it unless the TTL module is loaded), I get the following:

Code:
root@tomato-lab2:/tmp/home/root# iptables -t mangle -I POSTROUTING -o vlan2 -j TTL --ttl-set 65 -v
TTL  all opt -- in * out vlan2  0.0.0.0/0  -> 0.0.0.0/0   TTL set to 65
iptables: No chain/target/match by that name.


Notice I get the same output as you, *plus* an error message. See what I mean?

At least on tomato, I need to explicitly load the TTL module first, then it works.

Code:
insmod xt_HL


I always thought dd-wrt loaded this automatically, or it was in the firmware by default, but maybe there are exceptions. I can't guarantee that xt_HL is the module you need on dd-wrt. I'm only saying it works here for tomato.

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ddwrt-ovpn-split-basic.sh (UPDATED!)
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ddwrt-pptp-policy-based-routing.sh
Valchris
DD-WRT Novice


Joined: 28 Aug 2020
Posts: 2

PostPosted: Sat Aug 29, 2020 0:48    Post subject: Reply with quote
Wow! Thank you Eibgrad, that did the trick. Really appreciate the fast response!

eibgrad wrote:
On dd-wrt, the fact it reports adding the rule doesn't necessarily mean it did (yeah, weird). For space saving reasons, dd-wrt removes many error messages from the system (these days, w/ the amount of flash typically available, that shouldn't be necessary, but given the continued need to support legacy routers, it just is).

If I run that command on tomato (which I know doesn't support it unless the TTL module is loaded), I get the following:

Code:
root@tomato-lab2:/tmp/home/root# iptables -t mangle -I POSTROUTING -o vlan2 -j TTL --ttl-set 65 -v
TTL  all opt -- in * out vlan2  0.0.0.0/0  -> 0.0.0.0/0   TTL set to 65
iptables: No chain/target/match by that name.


Notice I get the same output as you, *plus* an error message. See what I mean?

At least on tomato, I need to explicitly load the TTL module first, then it works.

Code:
insmod xt_HL


I always thought dd-wrt loaded this automatically, or it was in the firmware by default, but maybe there are exceptions. I can't guarantee that xt_HL is the module you need on dd-wrt. I'm only saying it works here for tomato.
egc
DD-WRT Guru


Joined: 18 Mar 2014
Posts: 6360
Location: Netherlands

PostPosted: Sat Aug 29, 2020 8:15    Post subject: Reply with quote
On devices with 64 MB and higher flash ram it is loaded automatically,
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OpenVPN Policy Based Routing: https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=321686
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