[cisco-bba] ACLs on Virtual-Access templates

Tue Feb 3 03:01:57 EST 2009

Frank,

I checked and ingress ACL is the 1st feature evaluated, so it makes sense.

For logging, I think the feature is there.
Take a look in the command reference for uRPF:
http://www.cisco.com/en/US/docs/ios/ipswitch/command/reference/isw_i1.html#wp1013117

It has this text:
Unicast RPF events can be logged by specifying the logging option for the
ACL entries used by the Unicast Reverse Path Forwarding command. Log
information can be used to gather information about the attack, such as
source address, time, and so on.

So you should specify an ACL on the uRPF config with the log entry for any
relevant entries. Anything you permit on the ACL will be an exception to
uRPF. Anything denied would be dropped if uRPF fails (and only then).

Arie

On Tue, Feb 3, 2009 at 9:31 AM, Frank Bulk <frnkblk at iname.com> wrote:

>  Arie:
>
>
>
> I did some hunting around and the only stuff I did see showed that uRPF is
> processed before ACLs, so I'm a bit confused in that regard.  If you can
> verify, that would be appreciated.
>
>
>
> Using some debug commands I did identify a PPPoA connection that was
> spoofing traffic.  I removed off the inbound ACL on the Virtual-Template and
> I see that the strict uRPF is working:
>
> Router#sh ip interface Vi1.1120 | inc verif
>
>   IP verify source reachable-via RX
>
>    214 verification drops
>
>    0 suppressed verification drops
>
>    0 verification drop-rate
>
>
>
> Today I tried adding logging to uRPF:
>
> interface Virtual-Template1
>
>  mtu 1492
>
>  ip unnumbered Loopback11
>
>  ip verify unicast source reachable-via rx 126
>
>  ip mtu 1492
>
>  ip tcp adjust-mss 1452
>
>  no logging event link-status
>
>  peer default ip address dhcp
>
>  ppp mtu adaptive
>
>  ppp authentication pap
>
>  ppp ipcp dns a.b.c.d e.f.g.h
>
> end
>
>
>
> access-list 126 deny   ip any any log
>
>
>
> Unfortunately, it does not appear to be logging anything.  There's no 126
> lines, and I know that there's spoofed traffic coming through.  I re-applied
> my inbound ACL on the Virtual-Template, and I immediately saw this:
>
> Feb  3 01:27:45.326 CST: %SEC-6-IPACCESSLOGP: list 125 denied tcp
> 10.0.0.2(53070) -> 189.92.5.249(16016), 1 packet
>
> Feb  3 01:27:46.482 CST: %SEC-6-IPACCESSLOGP: list 125 denied tcp
> 10.0.0.2(52461) -> 24.82.113.224(22019), 1 packet
>
> It's strange.
>
>
>
> In regards to how I would like ACL-based logs to be documented; here's a
> typical log entry:
>
> Jan 31 15:23:21 a.b.c.d 38279: Jan 31 15:23:20.964 CST:
> %SEC-6-IPACCESSLOGP: list 125 denied udp 80.212.149.228(55190) ->
> 192.168.0.0(19427), 1 packet
>
> Jan 31 15:23:32 a.b.c.d 38287: Jan 31 15:23:31.476 CST:
> %SEC-6-IPACCESSLOGP: list 125 denied tcp 222.172.244.3(2047) ->
> 192.168.0.0(19427), 1 packet
>
> Jan 31 15:23:33 a.b.c.d 38288: Jan 31 15:23:32.784 CST:
> %SEC-6-IPACCESSLOGP: list 125 denied udp 151.48.173.200(25235) ->
> 192.168.0.0(19427), 1 packet
>
> Jan 31 15:23:36 a.b.c.d 38290: Jan 31 15:23:34.884 CST:
> %SEC-6-IPACCESSLOGP: list 125 denied udp 58.108.93.71(13502) ->
> 192.168.0.0(19427), 1 packet
>
>
>
> The feature request would be to log the interfaces, something like this:
>
> Jan 31 15:23:21 a.b.c.d 38279: Jan 31 15:23:20.964 CST:
> %SEC-6-IPACCESSLOGP: list 125 denied udp 80.212.149.228(55190) [ATM4/0.100
> 1/405 Vi1.1120] -> 192.168.0.0(19427) [Fa0/1], 1 packet
>
> Jan 31 15:23:21 e.f.g.g 38281: Jan 31 15:23:21.123 CST:
> %SEC-6-IPACCESSLOGP: list 125 denied udp 199.120.70.3(55190) [Fa0/1] ->
> 192.168.0.0(19427) [ATM4/0.100 1/899 Vi1.923], 1 packet
>
>
>
> Regards,
>
>
>
> Frank
>
>
>
> *From:* Arie Vayner [mailto:arievayner at gmail.com]
> *Sent:* Sunday, February 01, 2009 1:19 AM
>
> *To:* Frank Bulk
> *Cc:* cisco-bba at puck.nether.net
> *Subject:* Re: [cisco-bba] ACLs on Virtual-Access templates
>
>
>
> Frank,
>
> So, just to be sure - if you remove the ACL, does uRPF work as it should?
> I would assume (I don't have the time right now to make sure) that the ACL
> is evaluated before as it is part of the ingress packet processing, while
> uRPF is done later (close to the time when you also do a route lookup).
> Therefore, it would make sense for the ACL to take precedence.
>
> With regards to the log message, can you show me some example of what you
> actually get? I can then try and see if we can file an enhancement request.
>
> Thanks
> Arie
>
> On Sun, Feb 1, 2009 at 6:58 AM, Frank Bulk <frnkblk at iname.com> wrote:
>
> Just to add to that, is there a way that the Virtual-interface that's doing
> the spoofing can be identified?  The log entries for the ACL hits don't show
> anything but the spoofed IP, but I don't know which connection is doing it.
> Perhaps it's one PPPoA/E connection that's generating those spoofed packets…
>
>
>
> Frank
>
>
>
> *From:* Arie Vayner [mailto:arievayner at gmail.com]
> *Sent:* Saturday, January 31, 2009 3:49 PM
> *To:* Frank Bulk
> *Cc:* cisco-bba at puck.nether.net
> *Subject:* Re: [cisco-bba] ACLs on Virtual-Access templates
>
>
>
> Frank,
>
>
>
> uRFP should be the right way to block packets from the client as a
> source...
> After you connect, do you see the uRPF feature enabled on the
> Virtual-Access (show run interface and show ip interface)?
>
> Arie
>
> On Sat, Jan 31, 2009 at 11:35 PM, Frank Bulk <frnkblk at iname.com> wrote:
>
> Is there a way to build an ACL on a Virtual-Access template such that the
> connection can only use the IP address given to it by IPCP?
>
> I applied strict uRPF to the Virtual-Access template, but that didn't stop
> this kind of traffic:
>
> Jan 31 15:23:21 a.b.c.d 38279: Jan 31 15:23:20.964 CST:
> %SEC-6-IPACCESSLOGP:
> list 125 denied udp 80.212.149.228(55190) -> 192.168.0.0(19427), 1 packet
> Jan 31 15:23:32 a.b.c.d 38287: Jan 31 15:23:31.476 CST:
> %SEC-6-IPACCESSLOGP:
> list 125 denied tcp 222.172.244.3(2047) -> 192.168.0.0(19427), 1 packet
> Jan 31 15:23:33 a.b.c.d 38288: Jan 31 15:23:32.784 CST:
> %SEC-6-IPACCESSLOGP:
> list 125 denied udp 151.48.173.200(25235) -> 192.168.0.0(19427), 1 packet
> Jan 31 15:23:36 a.b.c.d 38290: Jan 31 15:23:34.884 CST:
> %SEC-6-IPACCESSLOGP:
> list 125 denied udp 58.108.93.71(13502) -> 192.168.0.0(19427), 1 packet
>
> Those source IPs aren't mine, and are targeting an RFC1918 address.  I'm
> blocking traffic originating from my PPPoA/E customers that use a source IP
> address outside my netblock or are targeting an RFC198 address using an
> inbound ACL on the Virtual-Access template, but it doesn't stop a a
> customer
> from spoofing their neighbor's IP address.
>
> I've had a basic ACL in place on our internet-facing Ethernet port (Cisco
> 7206VXR with NPE-400) for a long time, but I didn't having anything in
> place
> to block RFC 1918 addresses.  I could have applied the rules to the ACL on
> the Ethernet interface, but I've been told to apply an ACL as close as
> possible to the source of the traffic.
>
> To further complicate matters, I also use this router to route RFC 1918
> space for corporate needs.  I keep that "separate" by using source-based
> routing, but that didn't prevent PPPoA/E customers from sending a packet to
> the RFC 1918 space, even if the return packet never got back to them.
> Perhaps I should use a VRF for handling corporate, traffic, except that
> I've
> never done that before and I would need to spend some time learning.
>
> Frank
>
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