EIGRP Flashcards
What is DUAL?
Diffusing Update Algorithm; computational algorithm of EIGRP
What are two functions of DUAL?
- Guarantee loop-free backup routes.
2. Store all available routes to achieve rapid convergence
What multicast addresses are used by EIGRP RTP?
224.0.0.10, FF02::A
Describe the EIGRP Hello packet in terms of:
- Function
- Reliable or Unreliable transmission
- Sent unicast or multicast
- Neighbor discovery
- sent unreliably
- multicast
Describe the EIGRP Acknowledgment packet in terms of:
- Function
- Reliable or Unreliable transmission
- Sent unicast or multicast
- Acknowledge Receipt of Query, Reply, and Update Packets.
- sent unreliably
- unicast
Hello packets are sent unreliably in an effort to discover and maintain neighbor adjancencies. To which addresses are hello packets sent to?
IPv4: 224.0.0.10
IPv6: FF02::A
The default EIGRP hello interval and hold timer are dependent on interface bandwidth. What are the default hello and hold values for links faster than 1.544 Mb/s?
5s Hello 15s Hold (3x hello)
The default EIGRP hello interval and hold timer are dependent on interface bandwidth. What are the default hello and hold values for links slower than 1.544 Mb/s?
60s Hello 180s Hold (3x hello)
EIGRP update packets are always sent (reliably/unreliably). Are they sent as unicast or multicast?
Reliably, and can be sent as either unicast or multicast
EIGRP Query packets are always sent (reliably/unreliably). Are they sent as unicast or multicast?
Reliably, and can be sent as either unicast or multicast
EIGRP Reply packets are response to queries regarding other available routes. Are they sent unicast or multicast? Are they sent reliably?
Unicast, reliably
EIGRP Acknowledgement packets are “dataless” packets acknowledging receipt of an update, query, or reply. It is actually a “Hello” packet with a non-zero value in the Acknowledgment field. Are EIGRP ACKs sent unicast or multicast?
Unicast
What does “reliable delivery” imply about an EIGRP message?
Implies that an acknowledgment is expected in return?
In an encapsulated EIGRP message, what IPv4 address is likely to be found in the IP packet header?
Destination address 224.0.0.10
In an encapsulated EIGRP message, what will be the value of the protocol field in the IP packet header?
88
What two pieces of critical information are found in the EIGRP packet header?
Opcode and Autonomous System Number
What is the purpose of the opcode field in the EIGRP packet header?
The opcode field specifies the EIGRP message packet type.
An EIGRP packet header arrives with an opcode field value of 1. What does this imply about the EIGRP packet?
This is an EIGRP update packet
An EIGRP packet header arrives with an opcode field value of 3. What does this imply about the EIGRP packet?
This is an EIGRP query packet
An EIGRP packet header arrives with an opcode field value of 4. What does this imply about the EIGRP packet?
This is an EIGRP reply packet
An EIGRP packet header arrives with an opcode field value of 5. What does this imply about the EIGRP packet?
This is an EIGRP “Hello” packet if the value of the ACK field is 0. If the value is non-zero, it is an Acknowledgment.
What is the purpose of the EIGRP Autonomous System Number?
Allows tracking of the particular EIGRP process when multiple instances of EIGRP are active
An EIGRP packet arrives with a TLV field value of 0x0001. What information is expected to follow?
This value indicates EIGRP parameters follow, including K values and Hold time
An EIGRP packet arrives with a TLV field value of 0x0102. What information is expected to follow?
This value indicates information regarding an EIGRP internal route, including delay, bandwidth, subnet mask, and destination network
An EIGRP packet arrives with a TLV field value of 0x0103. What information is expected to follow?
This value indicates and EIGRP external route, including next hop, external protocol metric, delay, bandwidth, prefix, and destination network
What is the formula to calculate the default EIGRP metric?
((10,000,000/BW)+(sum of delays/10)) x 256
What is the default EIGRP delay value for Ethernet (10Mb) links?
1000
What is the default EIGRP delay value for Fast Ethernet links?
100
What is the default EIGRP delay value for Gigabit Ethernet links?
10
What is the default EIGRP delay value for FDDI links?
100
What is the default EIGRP delay value for serial links?
20,000
What is an EIGRP successor?
The router with the least-cost path to the destination network
What is the EIGRP feasible successor
EIGRP neighbor with a loop free-path to same destination as the successor, that also meets the feasibility condition
What is the EIGRP feasibility condition
Met when a neighbor’s reported distance to a given network is less than the local routers feasbile distance to that same network
What is meant by reported distance>
The metric that a router reports to a neighbor about it’s own cost to a network
An EIGRP router has just lost connectivity to a successor. What happens immediately?
DUAL examines topology table for a feasible successor
An EIGRP router has last connectivity to a successor. DUAL cannot find a feasible successor in the topology table. What happens next?
DUAL places the destination network in an active state
An EIGRP has lost connectivity to a successor. There was no feasible successor in the topology table, so DUAL placed the destination network in an ACTIVE state. What happens next?
DUAL begins querying neighbors for new route to the destination.
An EIGRP has lost connectivity to a successor. There was no feasible successor in the topology table, so DUAL placed the destination network in an ACTIVE state. Dual then queried other EIGRP routers for an alternative route to the destination. A neighbor did have a loop-free alternative route. What happens next?
DUAL selects that route as the new successor.
An EIGRP has lost connectivity to a successor. There was no feasible successor in the topology table, so DUAL placed the destination network in an ACTIVE state. Dual then queried other EIGRP routers for an alternative route to the destination. A neighbor did have a loop-free alternative route. DUAL installed that successor in the topology table. What happens next?
DUAL installs any feasible successors, if they exist in the topology table?
An EIGRP has lost connectivity to a successor. A feasible successor exists in the topology table. What happens next?
DUAL promotes the feasible successor to successor.
An EIGRP has lost connectivity to a successor. A feasible successor exists in the topology table. Dual promotes the feasible successor to successor. What happens next?
The successor is installed in the routing table
An EIGRP has lost connectivity to a successor. There was no feasible successor in the topology table, so DUAL placed the destination network in an ACTIVE state. Dual then queried other EIGRP routers for an alternative route to the destination. No neighbors had a loop-free alternative route. What happens next?
The destination network is removed from the topology table and routing table
An EIGRP has lost connectivity to a successor. A feasible successor exists in the topology table. Dual promotes the feasible successor to successor and installs its route in the routing table. What happens next?
DUAL installs feasible successors, if any into the topology table?
What conditions must be met for EIGRP routers to become neighbors?
- Must use same ASN
- Must pass authentication (if configured)
- Must have matching K values
