Problem on Looback (127.0.0.1)

Hey Folks.

Got a weird one. (I think, anyway.)

Running RedHat 9 (2.4.20-24.9)

I've got a problem with no traffic being allowed on the loopback (127.0.0.1)
interface. As part of troubleshooting I've installed an Accept-All iptables
policy, as well as turned off the iptables service but the results are the
same.

The interface is defined. ifconfig shows that.
I am able to ping 127.0.0.1.
There is a valid entry in the hosts file for localhost.localdomain.

Sendmail (used only locally) is queuing up boat loads of mail all of which
claim the connection was refused in 127.0.0.1
Attempted to ssh 127.0.0.1 - that reports, "ssh_exchange_identification:
Connection closed by remote host"
I don't see anything in syslog that would designate an error related to
attempted connections. When the firewall is running all connections are
127.0.0.1 are 'ACCEPTED'.

Any ideas about what could be blocking traffic on loopback?
....or am I looking in the wrong place?

Suggestions?

Thanks.
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> Hey Folks.
>
> Got a weird one. (I think, anyway.)
>
> Running RedHat 9 (2.4.20-24.9)
>
> I've got a problem with no traffic being allowed on the loopback (127.0.0.1)
> interface. As part of troubleshooting I've installed an Accept-All iptables
> policy, as well as turned off the iptables service but the results are the
> same.

Make sure that you've set an ACCEPT policy on the nat and mangle tables,
not just the filter table:

iptables -t nat --policy PREROUTING ACCEPT
iptables -t nat --policy POSTROUTING ACCEPT
iptables -t nat --policy OUTPUT ACCEPT

iptables -t mangle --policy PREROUTING ACCEPT
iptables -t mangle --policy INPUT ACCEPT
iptables -t mangle --policy FORWARD ACCEPT
iptables -t mangle --policy OUTPUT ACCEPT
iptables -t mangle --policy POSTROUTING ACCEPT

When I was building my firewall, I mistakenly set these to DROP and it
closed down my loopback interface. My PC was almost unusable for a week
until I found the problem.

Not sure what you mean by "turned off the iptables service".

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James News wrote:
> Hey Folks.
>
> Got a weird one. (I think, anyway.)
>
> Running RedHat 9 (2.4.20-24.9)
>
> I've got a problem with no traffic being allowed on the loopback (127.0.0.1)
> interface. As part of troubleshooting I've installed an Accept-All iptables
> policy, as well as turned off the iptables service but the results are the
> same.
>
> The interface is defined. ifconfig shows that.
> I am able to ping 127.0.0.1.
> There is a valid entry in the hosts file for localhost.localdomain.
>
> Sendmail (used only locally) is queuing up boat loads of mail all of which
> claim the connection was refused in 127.0.0.1
> Attempted to ssh 127.0.0.1 - that reports, "ssh_exchange_identification:
> Connection closed by remote host"
> I don't see anything in syslog that would designate an error related to
> attempted connections. When the firewall is running all connections are
> 127.0.0.1 are 'ACCEPTED'.
>
> Any ideas about what could be blocking traffic on loopback?
> ...or am I looking in the wrong place?
>
> Suggestions?
>
> Thanks.
Its also entirely possible that you have sendmail and ssh configured to
not accept connections from the loopback interface. Try going through
those configs to see if there are any interface restrictions set.

HTH
Neil

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