how to drop packets

[karthikeyan gopinathan]

hi

in my lan i see valid source IP addresses try to reach a invalid source IP addresses which is not available in the LAN.

for example in my firewall log

Deny inbound UDP from 172.16.1.3/1042 to 172.17.10.3/161 on interface inside

172.16.1.3 is valid but 172.17.10.3 is invalid or non existent

can you help create a acces list or packet drop config in switch so that this packet does not reach the firewall                  

[acampbell]

karthikeyan

Use you own names interfaces etc, but something along these lines.

!
ip access-list extended YOURLIST
deny udp host 172.16.1.3 eq 1042 host 172.17.10.3 eq 161
permit ip any any
!
!
!
interface vlan 16
ip address 172.16.1.1 255.255.255.0
ip access-group YOURLIST in
!

By the way UDP port is used for SNMP.
Looks like your device is trying to contact an snmp server.

Useful links:-

http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
http://www.cisco.com/en/US/products/sw/secursw/ps1018/products_tech_note09186a00800a5b9a.shtml#ipnamacl

Regards,
Alex.
Please rate useful posts.

[Joseph W. Doherty]

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Posting

BTW, an alternative to using an ACL, you might be able to route bad packets to a null interface, which also effectively drops them.