Network Design Considerations Involving PE and P Routers

Large networks such as those provisioned by ISPs are composed of and Provider Edge (PE) routers and Provider (P) routers, much like the network infrastructure found in MPLS networks. The PE routers in turn are connected to Customer Edge (CE) routers providing connectivity at the customer.

Here are some design considerations for such networks:

ISP network without P routers

When designing such networks, it is feasible to use only PE routers without incorporating P routers, but this is typically applicable to smaller networks. If you manage a network with roughly 5 routers, you can forgo P routers. However, in larger networks with around 100 routers, omitting P routers becomes challenging and costly due to the increased number of connections between PE routers and the lack of scalability.

Excluding P routers is generally inadvisable for service provider networks, except for very small cases usually not found in ISPs. P routers are instrumental in reducing network complexity by minimizing internal BGP sessions and allowing PE routers to concentrate on customer traffic management.

PE routers as BGP route reflectors

P routers are typically also used as route reflectors (RRs) for BGP deployments within such networks. Although PE routers can also serve as RRs, it is uncommon due to potential performance issues. It is generally advisable to use distinct devices for these roles to balance the network load effectively. RRs are optimally positioned near the network's core, while PE routers are located at the edge.

The strategic placement of RR routers depends on network size and layout. Ideally, RRs are positioned near the network's center to curtail the number of hops and bolster connectivity. In expansive networks, deploying multiple RRs—some potentially near the network's periphery—may be necessary for optimal function.

Connection to Internet

While both PE and P routers are technically capable of connecting to Internet Gateway (IGW) routers, best practices suggest that only PE routers should connect to IGWs. This is because PE routers, being at the edge of the service provider's network, handle customer traffic interfacing with the internet.

These guidelines are generalized; specific network requirements may differ based on size, traffic, and hardware capabilities.

Links:

https://forum.networklessons.com/t/service-provider-design-seeking-suggestion/52828/2?u=lagapidis