Picture this, you have been given a provisional WAN circuit using a T1, or multiple, in this particular use case; The provider is connecting you to its MPLS network, which provides you with an MPLS WAN address, an Internet WAN address.
This is simple for many out there, but it was not for me until not too long ago. I realize that in all of my turn ups I have been given an ethernet Hand off, and from there is just making a “Routing on a Stick” configuration and I will be calling it a day.
This case was different because how do you do trunks with a Serial interface?
Provisional connectivity is provided by the means of 3 T1’s, they are bundled to give you a rough 4.5 Mbps – You need to turn up the 3 circuits and bundle them into one Virtual interface.
Technologies such as Multilink interfaces are a great idea, but Multilink does not allow you to create Sub interfaces like you do with an Ethernet interface in the Cisco world.
Bridge connections are fine and could work, but why if the provider does not support them?
Bringing you back to Frame Relay
A Multilink Frame Relay interface will allow you to do this type of configuration. Since I’m not an expert and may confuse you trying to explain it in my own words, make sure you read this –> Wide-Area Networking Configuration Guide: Frame Relay, Cisco IOS Release 15M&T
Now if your scenario is like mine, you may have found limited options on the Support forums, which was my problem when turning this thing up the other day. but here is the configuration, I will try to explain the flow and the reasoning as best as possible so bear with me on this one
Turn up your T1 as you would normally do with a Data T1 controller
controller T1 0/0/0 cablelength long 0db channel-group 1 timeslots 1-24 ! controller T1 0/0/1 cablelength long 0db channel-group 1 timeslots 1-24 ! controller T1 0/0/2 cablelength long 0db channel-group 1 timeslots 1-24
Configure an MFR Interface (Multilink Frame Relay Interface)
interface MFR1 description WAN INTERFACE no ip address frame-relay lmi-type ansi
Configure your Sub-interfaces for the MFR Interface created earlier, Make sure you use the information give to you by the provider, or in the Cut-Sheet they give you, they will also refer you as to use VLAN XXX for Internet and VLAN XYZ for MPLS, make sure those numbers match your DLCI
interface MFR1.100 point-to-point description INET WAN ip address XX.XX.XX.XX XXX.XXX.XXX.XXX !!!! THIS IS PROVIDED BY THE ISP !!!! no ip redirects no ip unreachables no ip proxy-arp no cdp enable frame-relay interface-dlci 100 IETF ! interface MFR1.200 point-to-point description L3VPN WAN ip address XX.XX.XX.XX XXX.XXX.XXX.XXX !!!! THIS IS PROVIDED BY THE ISP !!!! no ip redirects no ip unreachables no ip proxy-arp no cdp enable frame-relay interface-dlci 200 IETF
And last but not least, make sure your Serial interfaces look like this
interface Serial0/0/0:1 no ip address encapsulation frame-relay MFR1 no arp frame-relay ! interface Serial0/0/1:1 no ip address encapsulation frame-relay MFR1 no arp frame-relay ! interface Serial0/0/2:1 no ip address encapsulation frame-relay MFR1 no arp frame-relay
Routing and everything else should happen automagically! (I say that because I remember playing with Frame Realy only from books and labs, not in real life)
Sometimes these T1’s or data channels won’t conform too quick, and this is fine, just make sure you unplug them and plug them back in, restart the interfaces or reload the router if possible, yes it happens.
A graphical representation of what we just did
I think this will help picture the scenario, hope it helps
What to look forward to?
Not much, this was only a deviation from my actual goal and wanted to share with you and all the people that may have never experienced this one, as always, feel free to reach out in case you have any questions.
About the Author:
Andres Sarmiento, CCIE # 53520 (Collaboration)
With more than 13 years of experience, Andres is specialized in the Unified Communications and Collaboration technologies. Consulted for several companies in South Florida, also Financial Institutions on behalf of Cisco Systems. Andres has been involved in high-profile implementations including Cisco technologies; such as Data Center, UC & Collaboration, Contact Center Express, Routing & Switching, Security and Hosted IPT Service provider infrastructures.