* Easing enterprise VPN routing complexity
If you have found it impractical or cost-prohibitive to learn and implement Border Gateway Protocol in order to use an Multi-protocol Label Switching-based IP VPN service, you’re gaining some options.
For example, if you use Cisco’s proprietary Enhanced Interior Gateway Routing Protocol internally, Verizon Communications will preserve your EIGRP routes across its MPLS IP VPN service. The carrier offers EIGRP as a standard routing option to its VPN service, along with BGP and Open Shortest Path First (OSPF).
Verizon can preserve your EIGRP routes whether you manage your premises routers yourself or whether Verizon is providing you with a managed router service, says Mike Tighe, director of advanced data services at Verizon. He observes, though, that the EIGRP service is most in demand where the customer is managing the router, since it’s a bigger headache for customers to deal with BGP when configuring and maintaining WAN-edge routers themselves.
“Many of our customers use Cisco [equipment] throughout their enterprises and use EIGRP,” Tighe says. “What would make their lives easier is if the routing protocol they use internally were the same one the service provider has implemented.”
In Cisco-centric shops, EIGRP is compelling as a routing option to MPLS-based IP VPNs because enterprises only have to configure their WAN routers for one protocol, their networks are easier to troubleshoot, and the likelihood of traffic taking the most efficient path is greater, Tighe says.
Technically, here’s how the setup works, according to Cisco:
Native EIGRP becomes the routing protocol running between the customer edge and provider edge routers. Without this support, normal redistribution of EIGRP into BGP at the provider edge would result in inter-site EIGRP routes appearing as external routes (rather than internal routes) in the target customer network site. External routes are less efficient.
Often, there is a “back door” EIGRP route between enterprise sites that doesn’t use the MPLS VPN, such as an ISDN backup link. Since that link is an internal link, traffic will always take it instead of the MPLS VPN unless the enterprise converts its entire network to BGP, which can be painful.
By supporting EIGRP, service providers preserve the enterprise customer’s EIGRP metrics across the MPLS VPN using Multi-protocol-BGP (MP-BGP) extended community attributes, making all the enterprise sites connected to the MPLS VPN look like one big internal EIGRP network.
At the peering site, BGP redistributes the route into EIGRP, which extracts the BGP extended community information and reconstructs the original route.
Cisco estimates that about 60% of enterprises use EIGRP as their interior routing protocol today.
