Actually standard packet filtering is supported by all Cisco products, and most others as well. Packet filters do not do state tracking. The packet filters you want will only work for TCP. You need to block everything else.
outbound on the interface to "the rest of the universe": permit tcp <source> any deny ip <source> any ... whatever other shit you want to permit to go out ... inbound on the interface from "the rest of the universe": permit tcp any <source> extablished deny ip any <source> ... whatever other shit you want to permit to go in ... Cisco (and others) have worked this way for about 40 years. -- Be decisive. Make a decision, right or wrong. The road of life is paved with flat squirrels who could not make a decision. >-----Original Message----- >From: cisco-nsp <[email protected]> On Behalf Of Emille >Blanc >Sent: Tuesday, 15 September, 2020 10:20 >To: Mike <[email protected]>; [email protected] >Subject: Re: [c-nsp] cisco ACL filter outbound only > >> Again, the cli seems to indicate support for all the things >> necessary, which includes the idea of 'established', which is why I ask >> if THIS platform does in fact do what the cli suggests: > >No, the ASR920 (Unless it's hiding in a recent IOS release), does not do >any kind of state tracking. You'll be better served looking at the ISR >or Firewall families for that. > >What you're seeing in the CLI is pretty commonplace these days - to be >fair, not just with Cisco - where an un-supported feature is 'left in' >the command line. > >If in doubt, try it. Worst case it won't work, and then you can bounce >the config off TAC to get one of their "unsupported configuration" canned >responses. :] >________________________________________ >From: cisco-nsp <[email protected]> on behalf of Mike ><[email protected]> >Sent: Tuesday, September 15, 2020 8:52 AM >To: [email protected] >Subject: Re: [c-nsp] cisco ACL filter outbound only > >On 9/15/20 8:08 AM, Brian Turnbow wrote: >>> It just seems to me that it is indeed possible using the above to put >it >>> together. Is this all just non-working on this platform? >>> >> The difference is in connection state. >> An ACL does not track it so you can do >> Permit tcp any any established >> Inbound or outbound on a port , but that will only check that the ip >packet has ack or rst set for the tcp session . >> I can still send you an inbound tcp packet with ack or rst set even if >it did not originate from "inside" and pass your filter. >> It will also not help in any way for udp etc >> The ACL does not know that a first packet was sent out so it should >await a response >> This is why you need a firewall be it on the router or external. >> >Hi, > > Again, the cli seems to indicate support for all the things >necessary, which includes the idea of 'established', which is why I ask >if THIS platform does in fact do what the cli suggests: > >rvhs-asr920(config-ext-nacl)#permit tcp 0.0.0.0 0.0.0.0 any ? > ack Match on the ACK bit > dscp Match packets with given dscp value > eq Match only packets on a given port number > established Match established connections > fin Match on the FIN bit > fragments Check non-initial fragments > gt Match only packets with a greater port number > log Log matches against this entry > log-input Log matches against this entry, including input interface > lt Match only packets with a lower port number > match-all Match if all specified flags are present > match-any Match if any specified flag is present > neq Match only packets not on a given port number > option Match packets with given IP Options value > precedence Match packets with given precedence value > psh Match on the PSH bit > range Match only packets in the range of port numbers > rst Match on the RST bit > syn Match on the SYN bit > time-range Specify a time-range > tos Match packets with given TOS value > ttl Match packets with given TTL value > urg Match on the URG bit > <cr> > >_______________________________________________ >cisco-nsp mailing list [email protected] >https://puck.nether.net/mailman/listinfo/cisco-nsp >archive at http://puck.nether.net/pipermail/cisco-nsp/ >_______________________________________________ >cisco-nsp mailing list [email protected] >https://puck.nether.net/mailman/listinfo/cisco-nsp >archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
