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Two t1's from same ISP need to be configed on a 2620 MLPPP? CEF? HELP!!

Posted on 2004-09-24
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Last Modified: 2012-05-05
Hi all,

       I have a client that before I started doing work for them ordered 2 t1's from Sprintlink..   They are to be bound, but I am very shakey on what the config should look like..

its a 2620XM 32megs  ios 12.2(8r)

So far after searching high and low, I have found that I can use MLPPP or CEF to accomplesh this...   Would anyone mind giving me a hand on the config, or atleast some direction on what I have to do, and what the ISP should be doing?

Thanks in advance!

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Question by:spiff637
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LVL 79

Expert Comment

by:lrmoore
ID: 12144985
If they are "bound" then you will be presented with a single external interface to an Inverse MUX. It could be a v.35 interface. It's just a single interface to the router, nothing special.
Or, you can simply have dual T1's, in which case you simply have dual static defaults and enable cef..

!
ip cef
!
interface serial 0/0
 descript line 1
  ip address x.x.x.x 255.255.255.x
!
interface serial 0/1
 descript line 2
  ip address x.x.x.x 255.255.255.x
!
ip route 0.0.0.0 0.0.0.0 serial0/0  <== I much prefer to use the upstream IP here vs the interface
ip route 0.0.0.0 0.0.0.0 serial0/1
0
 
LVL 11

Expert Comment

by:PennGwyn
ID: 12145264
> ip route 0.0.0.0 0.0.0.0 serial0/0  <== I much prefer to use the upstream IP here vs the interface

Most people do, but you have to do it this way if the connection is unnumbered or its address is assigned dynamically.  Cisco also points out that this saves a tiny amount of CPU which would otherwiase be spent looking up the mapping of ip address to interface, which *might* make a difference in a router running very near capacity.

Also, specifying the route by interface creates a routing table entry that comes/goes depending on whether the interface is up or down.  A route by address won't do that....

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LVL 79

Expert Comment

by:lrmoore
ID: 12145491
>A route by address won't do that....
Sorry, PennGwyn, I have to disagree on this point. Take this example config:

!
interface serial 0/0
 descript line 1
  ip address 4.5.6.2 255.255.255.252
!
interface serial 0/1
 descript line 2
  ip address 4.5.6.5 255.255.255.252
!
ip route 0.0.0.0 0.0.0.0 4.5.6.1
ip route 0.0.0.0 0.0.0.0 4.5.6.6

If the interface 0/0 drops, so does the first route because the 4.5.6.0/30 network is no longer "connected" and is not available.

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Author Comment

by:spiff637
ID: 12147152
Okay, so I confirmed on our order form that apparently it is to be bound, but I have no MUX yet..   Should I just go for dual t1's? This is mainly just an internet pipe..  some vpn's running on it, but nothing like a point to point setup..    
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LVL 79

Expert Comment

by:lrmoore
ID: 12147365
Dual T1's is actually better. Do you have the T1 DSU WIC's for the router?
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Author Comment

by:spiff637
ID: 12160458
I have 2 WIC-1t's already in it...      So the config will look something like your original comment?
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LVL 79

Accepted Solution

by:
lrmoore earned 250 total points
ID: 12161102
Yes, depending on the line encapsulation, you may have to have some additional configurations.
Do you know if you will use frame-relay, PPP, or HDLC on the T1? From SprintLink, I would assume that thay will be Frame-relay.
If that is the case, then it would look more like:

!
interface FastEthernet 0/0
 ip address 199.22.34.33 255.255.255.248  <== whatever Sprint assigns you
interface Serial 0/0
 encapsulation frame-relay
 frame-relay lmi-type ansi
!
interface Serial 0/0.1 point-to-poiint
  ip address 4.3.2.2 255.255.255.252
  frame-relay interface-dlci ##
!
 
interface serial 0/1
 encapsulation frame-relay
 frame-relay lmi-type ansi
!
interface Serial 0/0.1 point-to-poiint
  ip address 4.3.2.6 255.255.255.252
  frame-relay interface-dlci ##
!
!
ip route 0.0.0.0 0.0.0.0 4.3.2.1
ip route 0.0.0.0 0.0.0.0 4.3.2.5
!

done. Do you have a firewall behind this router that is doing your NAT/access restriction, or are you using this router for NAT?
Don't let Sprint tell you to use "ip unnumbered" - on the serial interfaces.



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Author Comment

by:spiff637
ID: 12183104
I'm working with Sprint right now, and will let you know.  Inlue of that I will go ahead and award you the points for such a complete answer.

Thanks again!
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