Roy's CCNA Notes

Day 25 - RIP & EIGRP

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Jeremy’s IT Lab lecture video:

Day 25 - RIP & EIGRP

Commands

Routing Protocol Information

General Configuration

  • The default-information originate command tells the router to advertise its default route to the other protocol neighbors.
  • The network IP-ADDRESS [WILDCARD-MASK] command tells the router to:
    • Look for interfaces with an IP address that is in the specified range and activate the routing protocol on them
    • Form adjacencies with the connected routing protocol neighbors
    • Advertise the network prefix of the interface (And NOT the prefix specified in the network command)
  • The passive-interface INTERFACE-ID command tells the router to:
    • Stop sending protocol advertisements out of the specified interface, but still keep on advertising the network prefix of the interface.
      • (This means the interface will stop sending out for example, RIP advertisements, on the specified interface. However, it’ll still advertise the network prefix of the interface like ‘192.168.0.0’ for example, to other RIP neighbors)
    • Used on interfaces which don’t have any routing protocol neighbors (ie. end-hosts or loopback addresses)

Routing Information Protocol (RIP)

Routing Information Protocol (RIP) is a distance vector IGP and an industry standard protocol.

RIP Info

  • Uses hop count as its metric, with each router equaling a hop.
  • Maximum hop count is 15.
  • RIP has three versions:
    1. RIPv1, used for IPv4
    2. RIPv2, used for IPv4
    3. RIPng (RIP Next Generation), used for IPv6
  • RIP uses two different message types:
    1. Request which is used to ask RIP-enabled neighbor routers to send their routing tables.
    2. Response which is used to send the local router’s routing table to neighboring routers.

RIPv1 and RIPv2

  • RIPv1
    • Doesn’t support VLSM or CIDR.
    • Only advertises classful addresses. (Class A, Class B, Class C)
    • Doesn’t include subnet mask information in advertisements (Response messages)
    • Messages are broadcast to 255.255.255.255
  • RIPv2
    • Supports VLSM and CIDR
    • Includes subnet mask information in advertisements
    • Messages are multicast to 224.0.0.9

Broadcast VS. Multicast

Broadcast messages are delivered to ALL devices on the local network.
Multicast messages are delivered only to devices that have joined that specific multicast group.

RIP Configuration

  • The router rip command is used to enter RIP configuration mode on the router.
  • The version 2 command switches RIP to version 2 which supports VLSM and CIDR
  • By default, RIP will advertise networks as classful networks. However, we can use no auto-summary in order to make it able to advertise classless networks.
  • network IP-ADDRESS [WILDCARD-MASK]
    • The command tells the router to:
      • Look for interfaces with an IP address that is in the specified range and activate RIP on them
      • Form adjacencies with connected RIP neighbors
      • Advertise the network prefix of the interface (And NOT the prefix in the network command)

Network command

  • The network IP-ADDRESS command doesn’t specifically tell the router which networks to advertise.
  • It tells the router to enable the specified routing protocol of the interfaces that fall within the specified IP range, and then the router will advertise the network prefix of the activated interfaces.

Enhanced Interior Gateway Routing Protocol (EIGRP)

Enhanced Interior Gateway Routing Protocol (EIGRP) is a distance vector IGP that was Cisco proprietary but had parts of it published for other vendors to use.

EIGRP Info

  • Reacts faster to changes in the network than RIP
  • Does not have the 15 hop count limit of RIP
  • Sends messages using multicast on address 224.0.0.10
  • The only IGP to be able to perform unequal-cost load-balancing (over 4 paths by default)

EIGRP Configuration

  • The router eigrp AUTONOMOUS-SYSTEM-NUMBER command goes into EIGRP configuration mode in the specified autonomous system group.
    • The AS (Autonomous System) number must match between routers, or they will not form an adjacency and will not share route information.
  • network IP-ADDRESS [WILDCARD-MASK]
    • The command will assume a classful address if you do not specify the mask.
      • Again, this will advertise the network prefix of the interface (And NOT the prefix in the network command)

EIGRP Metric

EIGRP uses bandwidth and delay to calculate metric by default.
Specifically, metric = bandwidth of the slowest link + the delay of all links

  • There are other options to change how the metric value is calculated, and they’re enabled and disabled through K values. By default, only bandwidth and delay are enabled, while the rest are disabled.
K value nameDefault value
K11 (Enabled)
K20 (Disabled)
K31 (Enabled)
K40 (Disabled)
K50 (Disabled)

EIGRP Router ID

The EIGRP router ID is selected through 3 methods, with priority being from top to bottom

  1. Manual Configuration
  2. Highest IP address on a loopback interface
  3. Highest IP address on a physical interface

EIGRP Terminology

Feasible Distance: This router’s metric value to the route’s destination
Reported Distance (aka Advertised Distance): The neighbor’s metric value to the route’s destination

Successor: The route with the lowest metric to the destination (Best route)
Feasible Successor: An alternate route to the destination (Not the best route), ==which meets the feasibility condition==

Feasibility Condition: A route is considered a feasible successor if it’s reported distance is lower than the successor route’s feasible distance

EIGRP Unequal-Cost Load-Balancing

In the show ip protocols command, a variance value can be found with a default value of 1

  • Variance 1 = only ECMP load-balancing will be performed.
    • Only routes with the same feasible distance as the successor will be used for load-balancing. (If a route has the same feasible distance as a successor, it can be considered a successor as well)
  • Variance 2 = Unequal-Cost Load-Balancing will be performed.
    • (Feasible Successor routes with a feasible distance up to 2x the successor route’s feasible distance will be used to load-balance)

Unequal-Cost Load-Balancing Note

EIGRP will only perform unequal-cost load-balancing over feasible successor routes. If a route doesn’t meet the feasibility condition, it will never be selected for load-balancing, regardless of the variance value.

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