What is sham link in OSPF?

The sham link is a logical intra-area link between VRF B on PE 2 and PE 3. OSPF creates an adjacency and exchanges LSAs across the sham link. As a result, OSPF sees both the path over the backdoor link and the path over the backbone as intra-area paths.

Why OSPF is used in MPLS?

Both the MPLS and OSPF protocols provide capability of addressing IP traffic management when it comes to large networks. The OSPF protocol is based on link state routing which means that every node in the network constructs a map of the network connectivity in the form of a graph.

What is OSPF super backbone area?

The super- backbone appears as another area to the CE-routers. s. Routes redistributed into MP-BGP from OSPF will appear as inter-area routes in other OSPF sites if the original route was an intra-area or inter-area route and as external routes if the original route was an external route.

What is OSPF domain ID?

A Domain Identifier (Domain ID) is defined as BGP Extended Community which is carried with VPNv4 routes between PE routers. This Domain ID is used to identify the OSPF instance from which it was redistributed into BGP. OSPF metric, OSPF Router-ID and OSPF Route-Type are also carried as BGP attributes of the route.

How does OSPF prevent loops?

Because inter-area OSPF is distance vector, it is vulnerable to routing loops. It avoids loops by mandating a loop-free inter-area topology, in which traffic from one area can only reach another area through area 0.

What is BGP blackhole?

The BGP blackhole community is attached to an announced prefix by an origin Autonomous System (AS) during a DDoS attack. Its purpose consists of signaling to a neighboring network that a neighbor router should discard all traffic destined for the received prefix with the attached BGP blackhole community.

Does MPLS require OSPF?

MPLS needs a standard IP connection in order to establish forwarding bases. Ensure that the routing protocol (OSPF or IS-IS) works correctly.

Does MPLS need BGP?

Only edge routers forward packets by looking up their destinations in the routing table. This means that edge routers are the only routers that need to have this information, so they need to run BGP. In some MPLS applications BGP is also used to distribute label information piggybacked in its updates.

What is P bit in OSPF?

The P-bit (P stands for propagate) can be found in the options field of an LSA type 7 and it tells the ABR if the LSA type 7 should be translated into a LSA type 5 or not. N-bit: this one is used in hello packets for OSPF NSSA routers. When the N-bit is not supported, the routers won’t become neighbors.

When using MPLS and OSPF What is use of PE router?

In either case, the OSPF router configured as a PE router in the BGP/MPLS VPN is always treated as an area border router (ABR) and functions as an area 0 router so that it can distribute interarea routes to the CE router.

What is DN bit in OSPF?

The DN bit is used to prevent loops. A PE does not process the received LSA that contains a DN bit. In a CE dual-homing scenario, this prevents the other PE from learning the same LSA from the CE and so prevents loops. The PE sets and checks the DN bit in Type 3, Type 5, and Type 7 LSAs.

What is capability VRF Lite?

1. ” capability vrf lite” will make OSPF process to install the routes even with DN bit set. 2. PE running VRF will set the DN bit when advertising to CE if OSPF is used for PE-CE routing. But CE is the device to check the DN bit when installing the route…

How does OPSF Sham link work in OSPF?

By using OPSF sham-link a virtual link is created between the two PEs allowing them to appear as a point-point link between OSPF. These links are able to fool/trick routers in the OSPF domain that this is a better path thus preserving the LSAs as type 1 or type 3.

How does Sham link work with MPLS VPN?

Because the sham-link is seen as an intra-area link between PE routers, an OSPF adjacency is created and database exchange (for the particular OSPF process) occurs across the link. The PE router can then flood LSAs between sites from across the MPLS VPN backbone.

How does OSPF select the best path over the backdoor link?

OSPF creates an adjacency and exchanges LSAs across the sham link. As a result, OSPF sees both the path over the backdoor link and the path over the backbone as intra-area paths. OSPF then selects the best path based on the metrics of the links and selects the sham link path, ensuring that the backdoor link is not used.

How is OSPF used in a PE router?

In some cases where Providers deliver MPLS links to customer locations , OSPF may be used as CE-PE routing protocol. PE router connected to the CE router collects all the routes in a VRF routing table based on the VRF applied to the incoming interface. These routes are then propagated across other PEs using MP-BGP.