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kryolla wrote: » do you have any interfaces with that mask or are getting any updates with that mask?
johnifanx98 wrote: » No. It just demos how router shows its routing table with one serial and two ehternet connected.
johnifanx98 wrote: » router A #show ip route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 3 subnets C 172.16.4.0 is directly connected, Serial 0 C 172.16.6.0 is directly connected, eth0 C 172.16.8.0 is directly connected, eth1 "172.16.0.0/24" confuses me. Should it be "172.16.0.0/16"?!
tech-airman wrote: » johnifanx98, Let me see if I can help you with your confusion. Generally speaking, a network address has two parts: a) Network part b) Host part. The private IP network address for a Class B address is 172.16.0.0/16. The network part being 172.16. and the host part being .0.0 based on the default mask of /16 or 255.255.0.0. Now, when you subnet a network, you borrow bits from the host part to accomplish that. So, when you read "172.16.0.0/24" it was of an "incomplete reading" issue. To read that line complete enough is "172.16.0.0/24 _is subnetted_..." So what the /24 refers to is NOT the default mask for the NETWORK 172.16.0.0 but instead it refers to the SUBNET mask for the SUBnetworks 172.16.4.0, 172.16.6.0, and 172.16.8.0. Does my explanation help?
Slowhand wrote: » Looks like your router is taking the three IP ranges and summarizing them. Not well, mind you, you can summarize those three much more efficiently than rounding up to /24, but it's definitely summarizing.
networker050184 wrote: » It is only giving you 172.16.0.0/24 because all your routes in that classful range (172.16.0.0./16) have a /24 mask. For instance if you had a few subnets with /25 masks only the statement would say 172.16.0.0/25 subnetted. When you mix different masks in the classful network then it will give you the classful network subnetted with the proper mask next to each entry.
networker050184 wrote: » No summarizing going on here. Its just the way the routing table displays the routes.
johnifanx98 wrote: » Just realized that RIPv1 has limitation of not advertising netmask. So maybe this way of displaying routing table has something to do with summarizing, but again not the summarizing I learned from textbooks. Is it possible?
johnifanx98 wrote: » Lots of help. Apologies I was not able to clarify my question enough. It seems like the language used by router is different than what I learned from textbooks. "172.16.0.0/24" does give me an wrong impression that there exist a network of 172.16.0.0 with netmask 25.255.255.0. However, I do not quite understand your explanation. Is there any official doc explaining this?
Network 172.016.00000000.00000000 Default Mask 255.255.00000000.00000000 Result 172.016.|00000000.00000000 172.016.|0.0
Subnetwork 172.016.00000000.00000000 Subnet Mask 255.255.11111111.00000000 Result 172.016.00000000.|00000000 172.016.0.|0
APA wrote: » The key is reading those output again and paying close attention to two lines... 1)172.16.0.0/24 is subnetted, 3 subnets 2)172.16.0.0/24 is variably subnetted, 3 subnets, 2 masks 1) is occuring because all your networks have a /24 network 2)is correct in saying it's variably subnetted but it should not be occuring with a /24.... as saying 172.16.0.0/24 is variably subnetted is incorrect when you have a /30 subnet that doesn't even belong to the 172.16.0.0/24 prefix... I think you may have found a bug... Output from my 1841 running 12.4T when using different prefixes from 172.16.0.0/16 172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks C 172.16.4.0/30 is directly connected, Loopback4 C 172.16.1.0/24 is directly connected, Loopback1 C 172.16.2.0/24 is directly connected, Loopback2 C 172.16.3.0/24 is directly connected, Loopback3 Hope this helps... What router and what image are you using?
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