paul.matthews Fri, 09/12/2008 - 06:54

We need a little more detail I am afraid! What routers, what is between them?

ThitPin1024 Tue, 09/16/2008 - 18:40

Those are cisco 1700 series routers.

btw them is 256 kbps leased line.

i have one ethernet port each router connected with IP-PABX and phones. Want to make VLAN for that network seperated from data traffic.


paul.matthews Tue, 09/16/2008 - 23:33

Ah! In that case you don't want VLANs! The concept is similar but on a WAN link they are referred to as Virtual Circuits. There are a couple of concepts that may get a little complex though, dependeing upon what you mean by keeping the traffic separate!

You could use frame relay for the link type, and create two DLCIs and run them on separate subinterfaces. The details are well documented on configuring frame relay, so you can do something like

int S0

enc frame-relay

int s0.100 point-to-point

Desc Voice Traffic

frame-relay interface-DLCI 100

ip add a.b.c.d m.a.s.k

int s0.101 point-to-point

Desc Data Traffic

frame-relay interface-DLCI 101

ip add e.f.g.h m.a.s.k

And similar at the other end. Please note I have typed this from memory, so there may be the odd typo!

That will give two logical circuits across the WAN, but if you just then include everything in the same routing process, you will not have segregation of traffic. Running two instances of OSPF and putting voice interfaces in one and data in the other will give a degree of separation, but will not guarantee it - both processes will add routing information to the same routing table. If you *really* want full separation you will need to look at VRF-Lite, which I don't think is available on the 1700.

ThitPin1024 Fri, 09/19/2008 - 03:31


Let's say I configured two virtual interface by using enc frame-relay.

Then how can i reserve dedicated bandwidth for each Interface traffic flow?

paul.matthews Fri, 09/19/2008 - 04:38

If bandwidth management is the aim, you don't need channels! This is where clear requirements are good.

If the whole aim is to manage bandwidth all you need do (says he flippantly) is look at the options with QoS. Separate circuits give "separation" (a little moot when you have them ending on the same routers.

QoS can be used in conjunction with circuits to do both bandwidth management.

The first thing you need to decide is exactly what behaviour you want. You can have multiple permutations of guaranteed minimum, maximum and prioritisation. If one type of traffic is not using its allocation, do you want the other to be able to use it?


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