Olá Pessoal,

Como estou estudando para BSCI fiz um grande resumão de cada um dos protocolos de roteamento para IPv4.

Um detalhe que deve-se observar é que este resumão foi feito em inglês (:S). Acreditem pessoal, eu consigo pensar melhor em inglês atualmente, especialmente para o estudo. Como o resumo é apresentado em tópicos é interessante para todos.

Para os que estão estudando para a CCNA é interessante dar uma breve olhada para ver o que tem por aí e aproveitar alguns tópicos que são escopo da certificação.

Um abração,

Maurício.

Segue abaixo:

Big Resume

EIGRP:
- Cisco proprietary and distance vector protocol (hybrid).
- Incremental updates.
- Uses Dual and crazy metric with K-values (1,3, Bw e DLY default)
- Establishes neighbors and mainting 3 tables (neighbor, topology, routing table).
- Neighbors must match: authentication, subnet, k-values, hello and dead timers.
- Only protocol that supports unequal cost load-balancing and backup routes (Feasible sucessor).
- If FS > AD the router can be a Feasible Sucessor.
- If there isn’t a feasible sucessor the router sends queryes for its neighbors asking for the route.
- Stuck-in-Active (SIA) is when a network is so big that it searches through it. To solve, router stub or summarization.
- Support ip summary address eigrp in the interface for summarizing the networks.
- Support keychain MD5 and plaintext authentication per interface.
- Support percentage of bandwidth usage, very used in PVC links.
- If you redistribute into EIGRP and don’t set a default-metric the route don’t to go to the routing table, because metric = infinite.

OSPF:
- Open standard protocol, uses the SPF algoritym by Djiskra.
- Link-state protocol. All the neighbors within an area have the same topology (database) table.
- Uses the cost of the links as the metric: 100/BW in MBps, or configured: ip ospf cost.
- Parameters for the neighborship are: area, area type, subnet, network type, timers, authentication
- Neighborship goes as: Down -> init -> 2way (parameters OK) -> Exstart (DR/BDR) -> Exchange (DBD) -> Loading (route exchange) -> Full
- Uses Areas and all of them must have a connection to the Backbone Area, area 0.
- ABR is the border between areas. ASBR is the border between an area and an external routing domain (Autonomous System Boundary Router).
- LSAs can be: 1,2 intra-area    3,4 between areas    5 external    7 nssa (only inside the NSSA area then turns into type 5).
- Areas can be Stub, totally-stub (cisco) and NSSA (not-so-stubby area).
— Stub: LSAs type 5 area substituted by a default route when injected within an area.
— Totally-stub: LSAs 3,4,5 … Set in the ABR, all the others can be stub.
— NSSA: When the ASBR is not in the backbone area this area generates type 7 LSAs. When they get to area 0 they transform into LSA type 5.

- Network types can be: Non-broadcast(NBMA),Point-to-multipoint (open); broadcast, point-to-point, point-to-multipoint nonbroadcast (CISCO).
— Non-broadcast (multiaccess): DR election, neighbor statically set, same subnet
— Point-to-multipoint: NO DR, neighbor auto, same subnet
— Broadcast: LAN (full mesh), DR, same subnet. CISCO MODE
— Point-to-multipoint nonbroadcast: Same as point-to-multipoint, but since it doesn’t support multicast neighbors STATICALLY configured. CISCO MODE
— Point-to-point: PPP, Subif, different subnets, neighbors auto. CISCO MODE

- Has Virtual-links that connects an Area through another to the Backbone area. area [transitarea] virtual-link [router-id].
- Has external metric-types. Type 2 maintain the same value. Type 1 is increased with the cost to each link as it passes by.
- Support summary address for ASBR. Area range for ABR. Both for summarizing the ip infrastructure.
- Support MD5 and plaintext authentication per interface.
- Default redistribution cost 20 (E2), BGP has 1(E2).

ISIS:
- ISO Routing protocol. Uses SPF algoritym.
- Uses NSAP addresses such as [49.0001].[0000.0000.0000].[00] AREA(49 is private) SYSTEMID NSEL(upper layer protocols). NET addr has NSEL 00.
- Routers are only in one area and communicate with a backbone router in another area. There area 2 level os routers and they keep different DBs:
— Level 1: Intra area routing. Keeps records inside an area so the routers must be inside the same area to become neighbors.
— Level 2: Inter area routing. Routers must be in different areas.
— Level 1-2: Is both! Keeps 1 database per Level. This is the router is the border of an area and communicates the intra routers with the inter.

- Is the only one that operates at layer 2.
- Uses TLV (Type, Length, Value) to carry information. This is a modular field, can have IP, routes, IPv6 and so on.
- Uses Metric, default for all links = 10.
- Routing decision goes as: Update, Decision, Forwarding, Receiving.
- Uses CSNP (complete SNP) for getting all the routes and PSNP to acknowledge. PSNP are for one or some routes.
- Has 3 tables: topology, neighbor, routing.
- Neighbors must match: Level, area (= for L1, != for L2), Unique System ID, timers, Authentication.
- On frame-relay must map the clns address.
- Uses links instead of networks. To activate the routing on an interface you must type ip router isis in the interface. isis circuit-type level-1, eg.
- Very bad in NBMA style networks, good to be fully meshed.
- Default for redistribution metric 0.

BGP:
- The only EGP that is a Path-vector routing protocol. If not otimized acts like RIP.
- Huge metric, treated as attributes. The order: Weight; Local_Pref; network or aggregate; AS_Path; i>E>?; MED; eBGP > iBGP… Lowest Router ID;
- Uses 3 tables: neighbor, topology, routing.
- Use autonomous systems. Hops are counted as ASs (AS_Path).
- Neighbors are discovered statically through neighbor 1.1.1.1 remote-as 11.
- iBGP runs within an AS whereas eBGP runs on different AS.
- Communicates through TCP 179.
- Next-hop addresses are always changed in eBGP peers, in iBGP peers the address is not changed. To change: neighbor 1.1.1.1 next-hop-self
- Peer groups are used to group configuration. Very used to configured iBGP peers (very like configs).
- Summarization is managed throuhg aggregate-address, and summary-only can be advertised.
- Very common to use route-maps to modify parameters or to filter routing updates in and outbound.
- If you have a multihoming connection (2 connections to the same provider) you peer to a loopback address. So, you must set the source as the
loopback. neighbor 1.1.1.1 update-source lo 0. BGP packets have a TTL of 1. You must increase this. neighbor 1.1.1.1 ebgp-multihop 2.
- Can have only one AS running in a router.
- Default for redistribution MED is given the IGP value.

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