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• ISO 10589 specifies OSI IS-IS routing protocol for CLNS traffic
• Tag/Length/Value (TLV) options to enhance the protocol A Link State protocol with a 2 level
• RFC 1195 added IP support
• IS-IS runs on top of the Data Link Layer
• Requires CLNP to be configured
• RFC5308 adds IPv6 address family support to IS-IS
• RFC5I20 defines Multi-Topology concept for IS-IS
• Permits IPv4 and IPv6 topologies which are not identical

• AIT: Authority and Format Identifier (the first octet of all OSI NSAP addresses—identifies format of the rest of the address)
• CLNP: Connection-Less Network Protocol (ISO 8473—the OSI connectionless network layer protocol—very similar to IP)
• ES: End System (the OSI term for a host)
• IS; Intermediate System(the OSI term for a router)
• ES-IS :End System to Intermediate System routing exchange protocol
• (ISO 9542—OSI protocol between routers and end systems)
• IS-IS : Intermediate System to Intermediate System routing exchange protocol (the ISO protocol for routing within a single routing domain)
• IS-IS Hello :A Hello packet (defined by the IS-IS protocol)
• LSP: Link State Packet (a type of packet used by the IS-IS protocol)
• TLV: Type Length Value

• Open standard (OSI)
• First developed by DEC and It was standardized by the ISO in 1992 communication between network devices which are termed Intermediate Systems by the ISO.
• Link-state routing protocol
• Classless
• VLSM and Manual summary
• Work on SPF or Dijkstra algonthm
• Incremental / trigger updates
• Updates are send as unicast /multicast (Layer 2)
• Metric= default (Cisco)
• Administrative distance = 115
• It is used by large ISP
• Protocol independent i.e. Support IP, IPX. hippie Talk

• Originally IS-IS was ECP for OSI layer, later developed to support TCP/IP called as DUAL IS-IS
  • Dual IS-IS works with this change features:
  • Function similar as any other IGP routing protocol
  • Fast convergence ( default hello = 10 sec . dead timer = 3 times of hello)
  • Stable
  • Make efficient use of bandwidth, memory &CPU resources

• Cisco supports only default metric

• e. Metric= 10 on any type of interface ( ex : serial/Ethemet/fastethemet/gigethemet)

• Narrow metrics
• Max value on interface can be 64 (6bit) and 1024 (10bit) per path in routing table
• Other venders support different types of metrics (default, delay, expense, error)

• ISIS has a 2 layer hierarchy
• Level-2 (the backbone)
• Level- 1 (the areas)
• IS-IS support three type of router levels

1. Level- 1 (LI) router (intra-area routing)
2. Level-2 (L2) router (inter-area routing)
3. Level-1-2 (L1L2) router (intra and inter-area routing)

• Manually Need to define IS-type
• Default is level 1 /Level 2

• Establishes neighbor ship with only LI and Ll/12 routers
• It acts like OSPF internal router (totally stub)
• Has the Level 1 LSDB with all routing information for the area
• It has a default route pointing towards nearest L1/L2 router
• LI should be continuous within a area.

• Establishes neighbor ship with only L2 and L1/L2 routers
• It act like OSPF Backbone router
• Has a Level 2 LSDB with all information about inter-area routing
• L2 should be continuous within a domain with other L2 orLl/L2 router

• Establishes neighbor ship with all LI , L2 and Ll/L2 routers
• It act like OSPF ABR
• Has two LSDBs:
• Level 1 for the intra-area routing
• Level 2 for file inter-area routing
• if the router has adjacencies to other areas, lt will inform the Level 1 routers (intra-area) it is a potential exit point for the area
• L1/L2 should be continuous within a domain with other L2 or Ll/L2 router

• ISIS does not have a backbone area as such (like OSPF)
• Instead the backbone is the contiguous collection of Level-2/ or Level 1-2 capable routers
• ISIS area borders are on links, not routers
• Each router is identified with Network Entity Title (NET)
• NET is an NSAP where the n-selector is 0

• The area address uniquely identifies the routing area and the System ID identifies each node
• All routers within an area must use the same area address
• An ES maybe adjacent to a level-1 router only if they both share a common area address
• Area address is used in level-2 routing
• System ID maybe the MAC address (CLNS) or IP address of an interface (IP world)
• System ID used in level-1 routing and has to be unique within an area (and of same length)
• System ID has to be unique within level-2 routers that form routing domain
• General recommendation: domain-wide unique System ID

1. Hello
2. LSP
3. CSNP
4. PSNP

• Both use the same method of topology abstraction
• Both use [ practically}the same flooding algorithm
• Both use [practically] the same Dijkstra algorithm
• Both provide IP routing information

• History
• Transport protocol
• PDU format
• Details of hierarchical routing

BGP Attributes

 BGP support a wide variety of path attribute, BGP chooses a route to a network based on the attributes of its path.

Four categories of attributes exist are as follows:-

• Well-know mandatory
• Well-known discretionary
• Optional transitive
• Optional non-transitive

Well-known mandatory attribute must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers. AS path, origin, and next hop.

Well-known discretionary must be recognized by all BGP routers and passed on to other BGP routers but need not be present in an update. Local preference

Optional transitive might or might not be recognized by a BGP router but is passed on to other BGP routers.

If not recognized, it is marked as partial. Aggregation, community.

Optional non-transitive If the BGP process does not recognize the attribute then it can ignore the update and not advertise the path to its peer. Multi-exit discriminator (MED), originator ID

 AS_Path attribute- this particular path attribute lists the autonomous system numbers in the end-to-end path.BGP uses AS_Path as its primary loop-prevention tool.

 AS_Path attribute is a well-known mandatory attribute. its list of AS through which updates are coming. The shortest AS_PATH list is more desirable.

Next_hop is a well-known, mandatory attribute next hop means IP address to reach next autonomous system because BGP is AS by AS routing protocol.

Origin attribute

 (i)  represent IGP

 (e) represent EBGP

 (?) represent incomplete

Weight Attribute is a cisco's attribute. its tell how to exit the AS, path with the highest weight is more desirable. weight is partial attribute, by default weight 0 learn route 32,769 for locally injected routes. its local to the router not advertise to any BGP peers.

Local Preference Attribute

Local preference define how to data traffic should exit from an Autonomous system. path with highest preference value is more desirable by default is 100, and the range 0 through 232  local preference is well known, discretionary attribute it is advertise only to iBGP neighbor within an Autonomous system.

R3#show ip bgp

BGP table version is 5, local router ID is 13.0.3.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

              x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric       LocPrf     Weight     Path

 r>i 10.0.0.0         11.0.0.1                 0                100            0            i

 r>i 20.0.0.0         12.0.0.1                 0                100            0            i

 *>  30.0.0.0         0.0.0.0                  0                                32768       i

 r>i 40.0.0.0         14.0.0.1                 0                 100           0             i