Nokia IRP - ISIS Focus

What value should the AFI be set to for locally administered addressing?

49 - Privately Assigned 47 - International Authority 39 - Single Country Authority

What is the IS-IS Protocol discriminator?

83 - hex, 131 - Binary

In IS-IS, If the receiver of the PSNP message has a newer instance of the relevant LSP, what happens?

PSNP is interpreted as a request for an Update

In IS-IS on a P2P Link, If a received PSNP or CNSP advertises a newer LSP, what happens?

PSNP is sent to request a new LSP

Which fields are in a Standard IS-IS packet header?

Protocol Discriminator = 131 Length indicator = Header Length Version/ Protocol ID =1 ID Length = System ID Length PDU Type = Type of IS-IS PDU Version -1 octet Resevered Maximum area addresses = # of permitted area addresses

In IS-IS for PSNP, if the receiver has a newer instance of the LSP in it LS database than the one it received, what happens?

Receiver will send a copy of the newer LSP back to the neighbor

In IS-IS, which of the following statements regarding an L1/L2 router is false?

A. An L1/L2 router can have neighbors in different areas. B. An L1/L2 router calculates separate SPF trees for the Level 1 and Level 2 topology. C. An L1/L2 router advertises its L2 routes to its L1 neighbors. D. An L1/L2 router sets the ATT bit in L1 LSPs to identify itself as an L1 router. Correct Answer: D

Which of the following TLV fields is included in an IS-IS Hello packet?

Area addresses TLV Intermediate system neighbors TLV Authentication information TLV IP Interface Address Protocol Support TLV Padding TLV

if two neighoring routers in the same area run both L1/L2, how many adjacencies and databases are established?

Two adjacencies: one for level 1 and one for level 2. Level 1 database Level 2 database

In IS-IS, which link type is used in CSNP for explicit acknowledge receipt of an LSP?

Used on a broadcast link

What is PSNP?

Used to request specific information about a network. contain a subset of LSPs in the database used to acknowledge one or more LSPs in P2P subnetworks Used to request transmission of specific LSPs on a broadcast network Transmitted to indicate the most recent instance of specific LSP received

In IS-IS when does the Adjacency state change from down to Initializing?

When a LAN Hello packet is received, the source MAC address of the LAN Hello is recorded in the adjacency database as the subnetwork point of attachment (SNPA), and the adjacency changes from down to initializing. The neighbor is known but bidirectional communication has not be verified.

In IS-IS on a P2P Link, if a received LSP has the same sequence number as an entry in the database, what happens?

it is ACK and interpreted as an ACK

In IS-IS on a P2P link, if a received LSP advertisement has the same sequence number as the entry in the database, what happens?

it is interpreted as an ACK and retransmissions of the LSP are stopped

In IS-IS on a P2P link, if the LSP or LSP advertisement is older, what happens?

An updated LSP is sent to the sender to update its database

What are the 3 circuit types in IS-IS field of the Hello Packet?

1 - means the originator accepts L1 adjacency only 2 - means the originator accepts L2 adjacency only 3 - means the originator accepts both L1 and L2 adjacencies

What is CSNP?

1 List every LSP in the database 2. Send out periodically to maintain database consistency 3. Several CSNPs can be sent at once 4. Leve 1 and Level 2 CSNPs

In IS-IS, on a Broadcast link, neighbors exchange CSNPs to describe the contents of their database. What happens?

1. DIS periodically sends multicast CSNPs other router compare contents of the database. it will send LSP or send a PSNP to request an LSP as necessary.

What are the NSAP Addressing Rules?

1. Level 1 Routing uses the system ID 2. Level 2 routing uses the system ID and area ID 3. 2 routers can not have the same NSAP address 4. 2 routers within an area cannot have the same system ID 5. AFT - set to 49 for locally administrered IS-IS 6. Area ID - min 1 byte 7. NSAP - min of 8 bytes (1 area, 6 for system, 1 for SEL)

What happens when a new DIS takes over?

1. Purge old pseudo node LSPs 2. Flood a new set of LSPs

in IS-IS on a Single Point to Point Link, what type of Adjacency is formed?

1. Single P2P hello used for both L1 and L2 adjacencies 2. One L1/L2 adjacency, instead of separate L1 and L2 like on broadcast links 3. Three way adjacency state (Down, Init and UP)

In IS-IS, How is a DIS elected?

1. The router with the highest interface priority 2. Tie Breaker: Highest Interface MAC address

Describe the IS-IS DIS (Designated Intermediate System)?

1.Sends the LSP information to our routers in the network 2. Separate Level 1 and Level 2 LSPs in the network 3. No Backup DIS exist. If the primary DIS goes down, new election takes place

What is the default cost for IS-IS?

10

If IS-IS wants to use OSPF Cost of 100 on a 1gig interface, what must be configured?

Configure reference-bandwidth, enable wide-metric-only and then provision metric under the Interface (wide-metric used on metrics over 100) Default is 10 Default metric value of 63 when wide-metric-only not provisioned

What happens in a Level 1 IS-IS if the Area ID TLV do not match?

Adjacency is rejected

In IS-IS on a broadcast Network, If the router receives an LSP advertisement that is older than the one in the database, what happens?

An updated LSP from the database is sent to the neighbors

How does Level 1 router build the local area topology?

Based on the System IDs Forward traffic to the nearest L1/L2 router

How does Level 2 router build the local area topology?

Exchange prefix information between areas build level topology based on area and system IDs forward traffic to appropriate areas based on SPF algorithm

How does IS-IS routers exchange updates on an Ethernet interface?

IS-IS routers exchange updates using Ethernet multicast packets

Which of the following best describes how IS-IS routers exchange updates on an Ethernet interface?

IS-IS routers exchange updates using Ethernet multicast packets

What is OSPF and IS-IS Max age?

IS-IS: 1200 without updates and 0 refresh LSP Packet OSPF: 0 and 1200 for refresh

What are the 3 Types of IS-IS Hello Packets?

Intermediate System-to-Intermediate System Hello End System Hello Intermediate System Hello

What happens ins IS-IS when the intermediate system is first attached to a link?

It begins sending hello packets, which discover and maintain neighbor adjacencies. If it receives hello packets back from any other IS, it begins building an adjacency with this new neighbor.

In IS-IS on a broadcast Network, If the router receives an LSP that is newer than the existing LSP in the database, or that is not in the database, what happens?

It is added to the database and flooded to the router's neighbors

In IS-IS on a broadcast Network, If the router receives an advertisement or an LSP that is the same sequence number as the entry in the database, what happens?

It is ignored

In IS-IS, if the receiver of the PSNP message has the same instance of the relevant LSP, what happens?

It is interpreted as an acknowledgement

In IS-IS, on a P2P links, neighbors exchange CSNPs to describe the contents of their database. If a router sees in a received CNSP an unknown LSP, or a more recent copy of a known LSP, what happens?

It sends a PSNP to its neighbor requesting a copy of the LSP

What types of routers can an IS-IS L1 router form adjacencies with?

L1 routers in the same area L1/L2 routers in the same area

What happens in a Leve 2 IS-IS in the Area ID TLV do not match?

L2 LAN hello is received, the router does not check the Area ID list; just accepts an Level 2 adjacency to the originating neighbor

What type of IS-IS Packet is generated by a L1 and L2 devices to convey information about neighbors and links.

LSP (Link-state PDU)

In IS-IS, when are LSP acknowledged?

LSPs are acknowledged with PSNPs on a P2P links No acknowledgements of PSNPs on broadcast links

What type of IS-IS adjacencies is formed when L1/L2 routers are in different areas?

Level 2 adjacencies

What is the term used for the updates sent by IS-IS?

Link State PDUs

If routers R1 and R2 have a Level 1 and Level 2 IS-IS adjacency, which of the following statements are true?

Routers R1 and R2 are in the same area Routers R1 and R2 will send a Level 1 Hello PDU and Level 2 Hello PDU, if the interface type between them is broadcast

In IS-IS, what is the function of the DIS (Designated Intermediate System)?

Sends the LSP information to our routers in the network

Which of the statements below best describes the pseudonode in an IS-IS network?

The DIS creates a logical node to represent a broadcast sub-network; this node is the pseudonode

When IS-IS is electing a DIS, what is used as the tie breaker on a Nokia 7750 SR, if the priorities are the same?

The Highest interface MAC address

Which of the following TLV fields is not included in an IS-IS point to point Hello packet?

The intermediate system neighbors TLV

In IS-IS when does the Adjacency state change from Initializing to up?

The neighbor router includes the SPNA in the IS Neighbors TLV in its own LAN Hellos. When the router sees its own interface MAC address in the IS Neighbors TLV of the neighbor's Hello Packet, it know that bidirectional communication has been verified. The adjacency state changes to UP.

In IS-IS, what happens to the DIS when a new router joins the network that has a higher priority?

The new router takes over as DIS

A Nokia 7750 SR receives a route via an IS-IS LSP with internal reach ability, and receives the same route via an OSPF type 5 LSA. If all protocol preferences are default, which route will be installed in the route table?

The route learned via IS-IS will be installed. IS-IS Internal preference 15 OSPF External Preference 180

In IS-IS on a broadcast Network, If the router receives an LSP advertisement in a PSNP or CSNP that is newer than the existing LSP in the database or that is not in the database, what happens?

The router requests the update LSP by sending a PSNP

In IS-IS database synchronization, each router compares each LSP described in the received CSNPs with the LSPs in its own database. Which of the following actions is taken if the database contains a newer copy of the LSP?

The router sends a copy of the LSP from its database to its neighbor

In IS-IS, on a P2P links, neighbors exchange CSNPs to describe the contents of their database. If the router sees in the received CSNP that the neighbor does not know about an LSP in the router's database or the neighbor has an older copy of an LSP, what happens?

The router sends the neighbor a copy of the LSP

The Receipt of an LSP on a broadcast link is always implicity acknowledged, why?

This is the default mechanism for acknowledging LSPSs as part of the LS database synchronization and maintenance procedures

In IS-IS, what happens when a router receives an out of date LSP?

Transmit an up to date LSPs

What is the source address of IS-IS messages?

always the data link layer address (MAC address)

In IS-IS on a P2P link, if a newer LSP is received, what happens?

database is updated newer LSP is flooded to other IS-IS neighbors PSNP sends back an ACK

What is the purpose of the Attached Bits (ATT) in IS-IS LSP Packet?

used in L1 areas to identify routers with L2 adjacencies. If this bit is set, that indicates that the IS can reach intermediate systems in other areas.

In IS-IS, which link types are used by PSNP to explicit acknowledgement receipt of an LSP?

used on a P2P link