topic Can a layer 4 policy block IM traffic in IOS firewall? in Network Security

Can a layer 4 policy block IM traffic in IOS firewall?

jopontes — Mon, 11 Mar 2019 14:29:40 GMT

Hi experts,

My customer wants to allow messaging just for certain users IP and block it for anybody else. His configuration is something like the following:

class-map match-all msn

match protocol imap

match access-group name Permited_MSN

ip access-list extended Permited_MSN

deny ip host 192.168.1.x

permit ip any any

policy-map msnmap

class msn

drop

interface BVI1

ip address 192.168.1.1 255.255.255.0

ip pim dense-mode

ip nat inside

ip virtual-reassembly

service-policy input msnmap

Doing a show policy-map, we never see matched packets being dropped.

Cisco1811W#show policy-map interface bvi 1

BVI1

Service-policy input: msnmap

Class-map: msn (match-all)

0 packets, 0 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: protocol imap

Match: access-group name Permited_MSN

drop

Class-map: class-default (match-any)

1722583 packets, 929916071 bytes

5 minute offered rate 612000 bps, drop rate 0 bps

Match: any

Should this configuration work? Can the router block MSN like traffic with a layer 4 policy or it is necessary to use zone-based with application policy?

Any comment on this is highly appreciated.

Re: Can a layer 4 policy block IM traffic in IOS firewall?

andrew.prince — Fri, 26 Dec 2008 17:05:01 GMT

The class map "MSN" will not work, The config is trying to match imap AND the access-list. IMAP has nothing to do with MSN.

Confirmation it is not working is in the policy-map lines:

"0 packets, 0 bytes"

To be honest using QoS (which is the policy map) is not the way to block this type of traffic. MSN has specific ports - depending on the version. The latest versions of MSN or Live Messenger will use HTTP.

HTH>

Re: Can a layer 4 policy block IM traffic in IOS firewall?

jopontes — Fri, 26 Dec 2008 17:47:11 GMT

Thank you Andrew!

I figured that this configuration had nothing to do with what the customer wants.

I am now configuring using the zone-based policies.

Configuring an Instant Messenger (IM) Policy

http://www.cisco.com/en/US/products/ps6441/products_feature_guide09186a008060f6dd.html#wp1566338

However, this seems to have only match-any clause, which does not give the option to tie an acl to take an action only on certain IP traffic.

Is there any other way to accomplish it?

Re: Can a layer 4 policy block IM traffic in IOS firewall?

andrew.prince — Fri, 26 Dec 2008 18:17:15 GMT

Mmmmm reading the link - I would kinda agree on that, however I have not had much experiance with the zone based firewall config. I do not have access to a router that supports this feature so cannot really see if multiple matches are available.

Sorry - perhaps another netpro has.

HTH>