This one deserves a homily. I can sleep tonight after solving this one. The age old question - how to get a /23 to propagate into classful /24 domain via redistribution.
I've been toying with this a while tonight. The problem - an "in use" interface - token ring or ethernet - has a /23 assignment. Let's call it 160.160.2.1 255.255.254.0 just for reference. This interface is in an OSPF or an EIGRP domain. The test is to redistribute this route into a RIP domain so that there is full reachability from anyplace in the RIP domain to any station in the OSPF / EIGRP domain. Oh yes, the RIP domain is a /24 domain. I tried the usual suspects. The rundown is as follows: 1) Setting up loopbacks with a /32 address. Problem - overlapping addresses 2) area range command in OSPF. Problem - Cisco's idea of summarization is the shortening of prefixes, not the lengthening. I tried variations of area range: area 222 range 160.160.2.0 255.255.255.0 area 222 range 160.160.3.0 255.255.255.0 area 222 range 160.160.2.0 255.255.254.0 not-advertise I thought maybe I could get around what OSPF was doing by using the no-advertise switch, and then using the area ranges with the /24's. The no-advertise suppresses all subnets of the particular range. There appears to be no way to circumvent this. 3) ip summary-address eigrp xxx etc interface command in EIGRP. Problem - summarization still only seems to like the shortening of prefixes, not the lengthening. Scratching my head. OK., let's try thinking out of the box, to coin a phrase. Well, one thing that keeps gnawing at me. RIP sends version 1, but receives version 1 and version 2 advertisements. OK. So how about on the redistribution router, I simply change the RIP version from 1 to 2? Can it be that easy? Apparently so, because it works. In the particular case, I have the Huge Subnet on Router_2: interface Loopback500 ip address 160.160.2.1 255.255.254.0 ip ospf network point-to-point ! router ospf 123 log-adjacency-changes network 160.160.2.0 0.0.1.255 area 222 network 160.160.254.2 0.0.0.0 area 0 Router_1 is the redistribution router. It shows the OSPF route in question: Router_1# Router_1#ir ospf 160.160.0.0/16 is variably subnetted, 20 subnets, 8 masks O IA 160.160.2.0/23 [110/26] via 160.160.255.2, 00:31:49, TokenRing0 On Router_1 I placed a loopback as follows: interface Loopback500 ip address 160.160.3.254 255.255.255.255 and I completed the task by making changes to the rip configuration: router rip version 2 redistribute ospf 123 metric 6 network 160.160.0.0 no auto-summary and then doing a rip summary address on the appropriate RIP interface: interface Serial0 ip address 160.160.127.1 255.255.255.0 no ip route-cache ip summary-address rip 160.160.2.0 255.255.254.0 ( summarizes the /32 on interface loopback 500 ) the result is that Router_4, a RIP ver 1 router, still sees the /23 network Router_4#ir rip 160.160.0.0/16 is variably subnetted, 30 subnets, 7 masks R 160.160.2.0/23 [120/6] via 160.160.127.1, 00:00:13, Serial0 OK, so that's one way to do it. I've seen discussion of using tunnel interfaces and secondary addressing as workarounds to this problem over on the CCIE list in the past. I know that several of the CCIE Lab study materials have tasks like this, leading me to believe that this is something one should add to the bag of tricks one needs when actually sitting in one of the testing centers. What is it my self help guru likes to say? "There is always a way." Peaceful evenings. Crisp autumn air. Goodnight everyone. -- Chuck Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=55773&t=55773 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]