1 T1 to 2 T1s

netcmh
netcmh used Ask the Experts™
on
Hello,

I have the following configured on a router with 1 T1. It's one of our branches which communicates with others and back to us over MPLS. It's working. No issues.

interface FastEthernet0/0
 ip address 192.168.1.254 255.255.255.0
 ip directed-broadcast
 ip flow ingress
 ip flow egress
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/0/0
 no ip address
 encapsulation frame-relay IETF
 service-module t1 timeslots 1-24
 frame-relay lmi-type cisco
!
interface Serial0/0/0.96 point-to-point
 ip address x.x.x.x y.y.y.y
 ip flow ingress
 ip flow egress
 frame-relay interface-dlci 96 IETF
!
interface Serial0/1/0
 no ip address
 shut
!

We're going to 2 T1s, and have recently added the s0/1/0 to the router.

I have verified with the ISP that they would like us to configure our router to multilink ppp.

I think that I need to do this:

interface Multilink1
description connected to ISP
ip address x.x.x.x y.y.y.y <- same as above in subinterface
no cdp enable
ppp multilink
ppp multilink fragment disable
ppp multilink group 1
exit

interface Serial0/0/0
description multilink 1 interface circuit xxxxxxxxxx
no ip address
encapsulation ppp
no ip mroute-cache
no fair-queue
no cdp enable
ppp multilink
ppp multilink group 1
exit

interface Serial0/1/0
description multilink 1 interface circuit xxxxxxxxxx
no ip address
encapsulation ppp
no ip mroute-cache
no fair-queue
no cdp enable
ppp multilink
ppp multilink group 1
exit

But, what happens to interface Serial0/0/0.96 point-to-point? I can't reboot for fear of loosing access to the router.

And, what happens to all the frame-relay stuff in the Serial0/0/0 & Serial0/0/0.96 point-to-point interfaces?

Please advise. Thank you.
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SouljaSr.Net.Eng
Top Expert 2011

Commented:
The subinterface will get automatically deleted when you add that serial to the multilink bundle.
Sr.Net.Eng
Top Expert 2011
Commented:
You best best is not to try to do this remotely unless you have some out of band method of accessing the router.
I don't and I can't. There is no other way, I've exhausted the possibilities :(
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SouljaSr.Net.Eng
Top Expert 2011

Commented:
I don't see how you would be able to assign the multilink the same ip address of the subinterface while it is active. Worst case perform a reload in x and try a change but don't save the config. If you get kicked out the router will reload with the previous config in the time you specify. I used to do this all of the time working on remote vpn sites.
The subinterface has nothing to do with your provider. This is 100% for your communications. I've worked with subinterfaces in a frame-relay network and our provider doesn't know which subinterface we used. The configuration you have looks very good.

You're key objectives is to build your multilink and then your serial interfaces must point to that multilink. One thing I'd recommend is you set the the interfaces for speed and duplex. Don't use auto/auto; it will likely be 100/full.
One final note, I have to tell you based on my experience with bonding T1s; it is cheaper to rip that out and replace with a metro ethernet. I don't know your situation or if anything of the sort is available. I replaced our bonded T1 (3mb) solution with a 10mb Metro E and saved $500 a month! It was a no brainer!

Best of luck!
SouljaSr.Net.Eng
Top Expert 2011

Commented:
I don't think the issue for the author is configuring the multilink, but doing it remotely is the issue.
Like Soulja said, issue the command reload in 120 then make your changes (but don't write them to memory). If the changes fail your router will reload at 120 seconds and everything will be undone.
SouljaSr.Net.Eng
Top Expert 2011

Commented:
Correct me if I am wrong but reload in 120 would be 2 hours?
You're correct. =) Hours and minutes.

the command is:

reload in mmm
or
reload in hhh:mm

Thank you both for your valuable input. I wasn't aware of Metro E - I am definitely going to look into that.

It's both actually - bonding and working remotely. I was aware of the reload in and was going to use it, but thank you for pointing it out, for future readers.

So, the moment I bundle the serial, the sub interface goes bye bye & no reboot is required?

I've got this router hooked up to the server at the location, and I'm hyperterminaled in - thinking that if I copy & paste the set of commands, then even if the connection breaks or hiccups, the commands would go through properly via the local connection from the server.

This is the set of commands I have planned:

interface Serial0/0/0
no ip address
encapsulation ppp
no ip mroute-cache
no fair-queue
no cdp enable
ppp multilink
ppp multilink group 1
exit
interface Serial0/0/0.96 point-to-point  <just in case
shut
exit
interface Multilink1
ip address x.x.x.x y.y.y.y <- same as the IP from the above subinterface
exit

I value your input, and no pressure, but I do this tonight :)

Thanks so much.
SouljaSr.Net.Eng
Top Expert 2011

Commented:
You can try it, but once you shut the subinterface you will be kicked out. Maybe the commands will be cached like you said. Regardless, make sure you do a reload in before starting. If successful MAKE SURE TO CANCEL THE RELOAD.  :)

yeah, can't forget that :)
just for notes:

reload in 10     < reboots router in 10 mins
reload cancel     < if all goes well, issue this command to cancel the reboot
show reload      < shows how much time you've got left
SouljaSr.Net.Eng
Top Expert 2011

Commented:
yes you are correct
Best thing to do is invest in a usb aircard modem & send it to the locations when you're upgrading it. that way you have a backdoor in just in case the config doesn't take.

Thanks to all for your advise.
SouljaSr.Net.Eng
Top Expert 2011

Commented:
Either that or for that serial not to be the only serial connection at the sight and you remote in on the other serial connection.
Just for posterity

Make sure you have the following:

service-module t1 timeslots 1-24

in your interface config

If the ISP hands you a Multilink IP, make sure you have accounted for that in your config for either static routing or BGP.

Quick question: If I needed to go up from a fractional to a full T1, is this all I need to do?

From:
int s0
service-module t1 timeslots 1-8

to:
int s0
service-module t1 timeslots 1-24

?
Thanks

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