ISIS Flashcards
What is the maximum and minimum length of the NET address
Maximum 20 bytes, minimum 8 bytes
What are the two levels of adjacency?
L1 and L2
Cisco IOS supports ISIS virtual link
False
In level 1 redistribution is allowed
True
Is Level 1 equivalent to OSPF stub area?
False, because in the stub area there are no external routes, Level 1 is equivalent to Totally not so stub area: Default route, Intra routes, Redistributed routes
In practice the L1/L2 router does not announce default route at level 1
True, it only sets the attached bit in the Link state Packets LSP
In the L1/L2 router there are two LSDBs, by default 1 per level
True
In a network with routers configured as default, SPF is executed only once
False, by default routers are L1/L2 so SPF is executed once for each level
L1 routes leak to L2 but L2 routes do not leak to L1 by default
True
ISIS supports the same types of interfaces as OSPF
False, only Broadcast and P2P
ISIS elects DIS and Backup DIS
False, there is no backup DIS
Once DIS is elected there is the possibility of preemption
True, it occurs by high priority of the interface, or by SNPA which is basically the MAC address of the ISIS process
Only one election occurs for both levels
False, two
DIS is elected on both types of interfaces
False, only in Broadcast
Adjacencies do not form in IP IP tunnels
True
Areas must match only in L2 adjacencies
False, in L1 areas
ISIS forms adjacencies on links of different network types
False
ISIS forms adjacencies on links of different MTU types
False
Default link cost is 10 and L2 routes are preferred over L1 routes
True, False
Metric style wide is default and required for MPLS TE
False, narrow. True
TLVs are used to encode metrics
True
ISIS by default does not support MPLS TE
True, due to narrow metrics
In case of metric style mismatch the adjacency does not come up
False, it comes up but the routes are not processed and do not appear in the RIB
Metric style wide is mandatory for IPv6 support
True
Neighbors running single and multi topology are compatible
False, adjacencies come up in IPv4 the routes are okay but the IPv6 routes are not
In single topology it is possible to have different costs for IPv6 and IPv4
False, in multitopology
In multitopology SPF is calculated twice
True
The NET address 00.0000.0000.0001.00 is invalid
False, it is valid
Passive interface lo0 without the ip router isis command allows the interface to be advertised
True
Check the syntax redistribute isis level-2 into level-1 route-map PERMIT-ANY
missing ip parameter as below: redistribute isis ip level-2 into level-1 route-map PERMIT-ANY
4 types of PDUs
•Hello PDU o ESH - End System Hello - Announces End Systems to an Intermediate system o ISH - Intermediate system Hello - Announces an Intermediate System (routers) to an End System o IS-IS Hello - Announcement between IS IS for adjacency formation • LSP PDU - Used to distribute link-state information • PSNP - Partial Sequence Number PDU - Used to ack missing parts of link state information • CSNP - Complete Sequence Number PDU :: Used to describe a complete list of LSP in the LSDB of a router
LSP on P2P links are sent as ______, on broadcast networks are sent as _______
Unicast, Broadcast
Level 1 and Level 2 adjacencies are not maintained via IIH o Default interval: ____ for non-DIS IS o For DIS the hello timer is ____ faster To quickly detect DIS failures
10s, 3x
If an LSP is valid and newer than the current one in the LSDB then it is accepted and timer set to ____ secs The timer is decremented sec by sec, when the value reaches 0 it is held for another ___ secs before being distributed as expired
1200, 60
2 types of Sequence Number PDUs (SNPs): _____ Contains a summary of the entire LSDB Routers exchange CSNP to compare their LSDBs Periodically multicast every 10 Secs by the DIS on the LAN On ptp links they are sent only initially after that only update LSPs which are acked by ______ o ______ Contains only a subset of LSP entries (like DBD?) Are used to request transmission of missing or new LSPs
CSNP, PSNP, PSNP
In single Topology the router does a consistent check and if the router does not have both address families configured then the v6 prefixes are not exchanged
True
