Category Archives: IP routing

routing policy configuration

Some time ago I wrote about local PBR and interface PBR.

It’s time to talk about routing policy, that is a different mechanism. Routing policy is applied to routing information and it is combined with routing protocols to form policies. PBR mechanism is applied to data flows and and packets are forwarded according to the configured policy.

Routing policy is a tool which can be used to filter routes and set route attributes, when importing routing information into OSPF, RIP, ISIS or BGP protocols. BGP can use routing policy to filter advertising routes as well. Routing policy defines which of the routes from the specific routing protocol are allowed to be imported into the target routing protocol. It can be also used to match routes or certain route attributes and to change these attributes when the matching rules are met.

Routing policy command syntax:

route-policy route-policy-name { permit | deny } node node

Continue reading

Advertisements

IP FRR on Huawei routers

What do we have in traditional IP networks?

Let’s assume that there is a fault at the physical or data link layers. Router sees that a physical interface becomes DOWN. After the router detects this fault, it informs upper layer routing system to update routing information. The convergence time is several seconds, what is critical for sensitive services.

That’s why IP FRR has been developed. After we configure IP FRR, a router doesn’t wait for network convergence but a backup link is immediately used to forward packets.

We have 2 scenarios of using IP FRR:

  1. To protect routers in public networks.
  2. To protect CE routers in private networks.

Let’s focus on the first one.

IP FRR topology Continue reading

BGP MED attribute on Huawei router

Some time ago I published article about BGP local preference attribute. Today I’d like to show you how to configure BGP MED attribute.

What is it for?

The multi-exit discriminator MED determines an optimal route for incoming traffic of an AS. When a BGP device obtains multiple routes to the same destination but with different next hops from EBGP peers, the BGP device selects the route with the smallest MED value as the optimal route. Simply saying, configuring MED attribute, we would like to show the next hop for traffic coming from EBGP peer. The MED attribute is exchanged only between two neighboring ASs. The AS that receives the MED attribute does not advertise it to any other ASs.

Let’s look at typical scenario for MED attribute configuration:

BGP MED topology Continue reading

OSPF stub area on Huawei router

Instead of transmitting learned AS external routes, area border router, in a stub area, generates a default route and advertises the route to non-ABRs in the stub area. In short, stub area reduces entries in the routing table of ABR and the amount of routing information to be transmitted.

We have to remember that:

  • The backbone area cannot be a stub area
  • All routers in a stub area need to be configured using stub attributes
  • The ASBR cannot exist in a stub area
  • Virtual links cannot be configured in stub area.

Let’s try to configure a simple lab. We would like to see what happens if AREA1 becomes a stub area.
Continue reading

local PBR on Huawei AR routers

Some time ago I wrote about interface policy-based routing PBR. Today I will show you example of local PBR configuration on Huawei AR routers. Local PBR allows you to forward packets through different interfaces or to different hops. Unlike interface PBR, local PBR is used for locally generated packets and classifies packets based on source addresses or packet lenghts.

Let’s look at the topology and configure as follows:

  1. Locally generated ICMP packets (with the size of 70-1300 bytes) will be sent to next hop IP address 172.16.0.2.
  2. Locally generated ICMP packets (with the size of 1301-1500 bytes) will be sent to outbound interface GE0/0/1.

local PBR on Huawei routers topology

Continue reading