The Attribute field within the IS-IS LSP header contains which of the following flags? (Choose four)
A.
IS-Type
B.
Overload (LSPDBOL)
C.
Pseudonode (PN)
D.
Attached (ATT)
E.
Fragment (Frag-Nr)
F.
Partition (P)
Explanation:
Partition Repair (P): Although this bit exists in both L1 and L2 LSPs, it is relevant only in L2 LSPs.
When this bit is set to 1, it indicates that the originating router supports the automatic repair of
area partitions. Cisco IOS does not support this feature; it always originates LSPs with the P bit
set to 0.
Attachment (ATT): A 4-bit field indicating whether the originating router is attached to one or more
areas.
Although this bit exists in both L1 and L2 LSPs, it is relevant only in L1 LSPs originated by L1/L2
routers to indicate that it is also a L2 router, which is a potential exit to reach other areas. Reading
from left to right (bits 7 – 4), the bits indicate the Error metric, the Expense metric, the Delay
metric, and the Default metric. Cisco IOSsupports only the default metric, so bits 5 – 7 are always
0.
Overload (OL): The Link-State Database Overload bit. This bit is often set to 0. A router set this bit
on its LSPs when unable to store the entire LSDB. Routers receiving an LSP with the OL bit set
will not use the originating router as a transit router as its routing table is incomplete, which may
result in suboptimal routing and even routing loops; but they will still forward packets destined to
the directly connected networks or interfaces of the originating router.
IS Type A 2-bit field indicating whether the originating router is an L1 or L2 IS.
01 – L1; 11 – L2; 00 and 10 are unused values.
An L1/L2 router sets the bits accordingly upon its L1 and L2 LSPs.
