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IETF to explore new routing technique

Cisco engineers propose adding tunneling overlay to edge, core routers

By , Network World
March 26, 2009 03:02 PM ET

Network World - SAN FRANCISCO – The IETF is forming a new working group to address scalability issues in the Internet's routing system caused by companies splitting their network traffic over multiple carriers, a practice called multihoming.

The new working group will build upon a base proposal from a team of Cisco engineers to create a new tunneling mechanism that will be used by the Internet’s edge and core routers.

The new mechanism — dubbed LISP for Locator/Identifier Separation Protocol — is designed to reduce the number of entries in the routing tables stored in the core routers operated by ISPs.

LISP logically separates a block of IP addresses that a company advertises out to the global Internet via its edge routers into two functions: one for identifying the systems using the IP addresses, and the other for locating where these systems connect to the Internet. This separation allows LISP to aggregate the location information, so less of it needs to be stored in the core routers.

LISP works through dynamic encapsulation. Every packet that enters the core routers gets a new IP wrapper that carries information about the destination service provider network, not the end-user IP address. The wrapper is removed from the packet when it gets to the destination service provider.

LISP would operate in conjunction with the Border Gateway Protocol (BGP), which is the primary communications mechanism between edge and core routers.

"The problem we have is that IP addresses are assigned to hosts, and they're not assigned topologically," says Dino Farinacci, a Cisco Fellow and Senior Software Engineer and one of the authors of the LISP proposal. "This means the core routers on the ISP networks have to carry all of the site-specific routes. We're trying to separate the topological significance of the address from the address allocation procedures…and that will reduce the size of the BGP routing table."

LISP proponents say the technique also would make it easier for companies to switch carriers without having to acquire new IP addresses because the identification function would remain constant even if the location information changes. And LISP offers companies additional traffic engineering capabilities, backers say.

"More enterprises want to multihome their sites, and they want to do it in a low op-ex way," Farinacci says. "Today they have to do it with heavy overhead. They have to use BGP, and they have to publish routes into the core. With LISP, we’re putting the routing policy at the edge where the customers can control the bandwidth they pay for."

Cisco engineer Darrel Lewis, co-chair of the LISP working group, said a key point about LISP is how sites can negotiate their multi-homing policy in an independent, open manner.

LISP developers say the protocol will be deployed as a software upgrade to edge routers, and that no hardware upgrades will be required to run it. They say it will be incrementally deployable and can work with the current version of the Internet Protocol, known as IPv4, or a long-anticipated upgrade known as IPv6.

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