Setting up three routers via serial interfaces for LAB purposes all on the same subnet daisy chained

[jorge75medina]

I have two Cisco 2811 and once Cisco 2821 in my home lab. This is the topology: Router 1, 2 and 3. Router 3 has a WIC1T card, ip address 10.1.1.4/29 which is connected via DTE/DCE serial to router 2 with another WIC1T card ip address 10.1.1.3/29. On the same router, Router 2, I have another WIC1T card on serial port S0/1/0 with ip address 10.1.1.2/29 connecting to router 1 with yet another WIC1T card and DTE/DCE cable on serial interface S0/1/0 with ip address 10.1.1.1/29. All daisy chained and on the same subnet. I cannot however ping from router 1 , 10.1.1.1 to anywhere else in the topology. Does a router with two serial interfaces have to be on different subnets for this three router daisy chain to work? How do I set this up so I can set up all three routers so I can ping across all three of them? Please help! it only works if the router with the two serial interfaces are on different subnets. No routing protocols enabled. Should I try EIGRP??

[acampbell]

Jorge,

When you configured router 2 you should have an alert to tell you
that you have overlapping ip addresses.

On your 1st link R3 -- R2 you have used 10.1.1.0/255.255.255.248
Your available addresses are .1 to .6.

If you are just using Cisco HDLC or PPP for your link encapsution you cannot use
this subnet again on that router/network

Break your subnet down into 2 x /30 networks

R3 --- R2
10.1.1.6 & .5/255.255.255.252

R2 --- R1
10.1.1.2 & .1/255.255.255.252

Hope this helps
Reagards
Alex

[jorge75medina]

Thanks Alex. I will surely try this tomorrow. I'm sure it will work. So to echo your suggestion, break it down into two /30 networks using VLSM type addressing and it wont overlap. Its funny, I didn't get an overlap alert when I did this and I also had all interfaces in an up/up status as well. The link between Router 1 to 2 worked fine but the link from R2 to 3 showed up/up, no overlap syslog message and it didn't ping through. IOS and its funny quirks. ;)

[NeilGouws]

Just a thought, you don't have to use the Serial cards, all those routers have multiple FastEthernet Ports.

But let's continue with the way you were working

And remember to set the clock-rate on the DCE side of the Serial interface

For a Point to Point link you only need 2 IP Addresses, therefore:

10.1.1.0/30   - R1<--->R2

10.1.1.4/30   - R2<--->R3

Encapsulation must match on both sides of the P-2-P connection, either HDLC or PPP

R1<--->R2<--->R3

R1:

int Serial 0/1

  ip address 10.1.1.1 255.255.255.252

  encapsulation hdlc

!

ip route 0.0.0.0 0.0.0.0 10.1.1.2 name Default-Route

R2:

int Serial 0/1

  ip address 10.1.1.2 255.255.255.252

  encapsulation hdlc

int Serial 0/2

  ip address 10.1.1.5 255.255.255.252

  encapsulation hdlc

R3:

int Serial 0/1

  ip address 10.1.1.6 255.255.255.252

  encapsulation hdlc

!

​ip route 0.0.0.0 0.0.0.0 10.1.1.5 name Default-Route

That's the basics, it should work now.

R2 doesn't need static routes, because both networks are directly connected to it

If you want to do EIGRP, then remove the default routes on the routers and add the following config

R1:

router eigrp 1

  no auto-summary

  network 10.1.1.0 0.0.0.3

R2:

router eigrp 1

  no auto-summary

  network 10.1.1.0 0.0.0.3

  network 10.1.1.4 0.0.0.3

R3:

router eigrp 1

  no auto-summary

  network 10.1.1.4 0.0.0.3

Have lots of fun !!!

[Dan Lukes]

You are asking in community with no relationship to the topic. You are lucky as other CSC members answered despite of it. Unfortunately, their time will be wasted if further users with same issue will not find the answer.

So please use blue [ EDIT ] button to move this thread to Network Infrastructure -> WAN, Routing and Switching

Also, consider rating of valuable answers. It's way to say "thank you for your response". In advance, it will help others to find valuable answers.

Thank you.

[jorge75medina]

Im not sure who you are, but am I seriously getting reprimanded for no choosing the right community by mistake? Are you the webmaster? are you a disciplinary administrator for this thread? Help me here........................................................

[Dan Lukes]

It's not matter of title of any kind. Consider me just other user of CSC forum. And no one is going to punish you.

I just kindly asked you to move this thread from the inappropriate community to the appropriate one. It's just matter of thoughtfulness - to those users who spent their time to respond you as well as to those future users facing similar issue.

[jorge75medina]

Thank you for clarification, however, you came across (and I am sure a few other people will agree) very abrasive, demanding and authoritarian. Furthermore, in the interest of the integrity of this thread and the topic, I will move this to the proper thread. It is just a thread were people ask for help, not a matter of procedure.