Which two provide intra-area routing services?

Which two provide intra-area routing services? (Choose two.)

A.
L1 ES

B.
L2 IS

C.
L2 ES

D.
L1 IS

E.
L1/L2 IS

Explanation:
An IS-IS network is termed a domain, analogous to an autonomous system (AS) in TCP/IP.
The following shows IS-IS within the domain as a two-level hierarchy:
• Level 1 (L1) ISs, closely equivalent to OSPF internal non-backbone routers, are
responsible for routing to ESs inside an areA. L1 ISs enable communication between ESs in
an areA. L1 routers are also referred to as station routers because they enable stations to
communicate with each other and the rest of the network. A contiguous group of L1 routers
defines an areA. The L1 routers maintain the L1 link-state PDU database (LSPD), which
defines the picture of the area itself and the exit points to neighboring areas.
• Level 2 (L2) ISs, closely equivalent to backbone routers in OSPF, route between
areas only.
• Level 1 and Level 2 (L1L2) Intermediate ISs, closely equivalent to area border
routers (ABRs) in OSPF, route between areas and the backbone. They participate in the L1
intra-area routing and the L2 inter-area routing.
L1L2 routers support an L1 function to communicate with the other L1 routers in their area
and maintain the L1 LSP information in an L1 LSPD. They inform other L1 routers that they
are an exit point for the areA. They also support an L2 function to communicate with the rest
of the backbone and maintain an L2 topology database separately from their L1 LSPD. IS-IS

does not share the concept of an Area 0 with OSPF. An IS-IS domain appears as a set of
distinct areas interconnected by a chain of L2 routers, weaving their way through and
between the Level 1 areas.