Enhanced Interior Gateway Routing Protocol
AD
Summary 5
Internal 90
External 170
Multicast address 224.0.0.10
Port 88
- Defines same basic topology information about each route for each unique prifix length
- the basic information includes the prefix, prefix length and metric information and few other details. EIGRP neighbors exchange topology information, each router storing the learned topology information in there respective EIGRP topology table.
- to get the process started each EIGRP router needs to add topology data for some prefix so it can then advertise these route to its EIGRP neighbor
- A router EIGRP process adds subnet to its local topology without learning the topology data from an EIGRP neighbor and three sources
- Prefixes of connected subnets for interfaces on which EIGRP has been enabled on that router using network command
- Prefix of connected subnets for interfaces referenced in an EIGRP neighbor command
- Prefix learned by the redistribution of routes into EIGRP from other routing protocols
EIGRP Update Message(HUQRA)
Hello
Update
Query
Reply
Acknowledge(ACK)
Update and ACK are used as two messages as part of the topology data exchange process
Update message contains the topology information whereas ACK receipts of the update packet
Update message contains following information
- Prefix
- Prefix lenght
- Metric components: bandwidth, delay, reliability and load
- Non-metric items: MTU and hop count
default setting for load -1 reliability- 255
EIGRP for delay add the delay value of the interface update received on to the delay value received
for bandwidth EIGRP simply chooses the lowest bandwidth compairing the bandwidth of its own interface with the bandwidth listed in the received EIGRP update.
EIGRP Update Process
- when a neighbor first comes up the router exchange full updates meaning the router exchange all topology information
- after all prefixes have been exchanged with a neighbor the update cease with that neighbor if no change occurs in the network, there is no periodic reflooding of topology data
- if something changes the router sends partial updates about only the prefix whose status or metric component have changed
- if a neighbor fails and then recovers or new neighbor adjacency are formed full update occurs over these adjacency.
- EIGRP uses split horizon rule on most of the interfaces by default
- To send update EIGRP uses the Reliable Transport Protocol(RTP) to send the updates and confirm receipt. The RTP manages the delivery and reception of EIGRP packets. Reliable delivery means that delivery is guaranteed and that packets will be delivered in order. Guaranteed delivery is accomplished by means of algorithm known as reliable multicast, using the reserved class D address 224.0.0.10. Each neighbor receiving a reliably multicast packet unicasts an acknowledgment.
- EIGRP routes must be reachable using layer 2 frames before they can exchange hello messanges and become EIGRP Neighbor.
- EIGRP router builds IP routing table entries by processing the data in the topology table
Metric Calculation
EIGRP topology table entry for a single prefix/lenght list the one or more possible routes, each route list the various component metric value-bandwidth, delay and so on. Additionally for connected subnets the database entry list an outgoing interface.
for route not connected to the local router, in addition to an outgoing interface the database entry also lost the IP address of the EIGRP neighbor that advertise route.
An EIGRP router does its calculation both from its own prospective anf from the prospective of the next hop router of the route.
The two values are called FD and RD
Feasible Distance(FD):- Integer metric for the route from the local perspective, used by the local router to choose the best for the prefix
Reported Distance(RD):- Integer metric for the route from the neighboring router's prospective(the neighbor that told the local router about the route). Used by the local router converging to new routes.
Route use teh FD to determine the best route based on the lowest metric and use the RD when falling back to an alternative route when the best fails.
when a route has calculated the integer FD for each possible route to reach single prefix/length that router can then consider adding the lowest metric route to the IP routing table.
FD- end to end metric
RD- metric reported by neighbor to a particular destination
FC= RD
RD of feasible successor must be less than FD of successor
Slower the bandwidth worst the metric.
Metric= 256x(107/slowest-bw)+cumulative delay)
Tuning Metric
- Setting interface bandwidth
- Setting Interface Delay
- configuring K values
- adding metric in offset-list
bandwidth is in Kb/sec
delay is in 10s of microsecond
Composite Cost Metric = (K1*Minimum Throughput) + (K3*Total Latency)
Minimum Throughput = (107* 65536)/Bw), where 65536 is the wide-scale constant.
Metric weight(K Values) from 0-255
k1 and k3 are 1 by default
EIGRP requires that two routers k-value match before those routers can become neighbor
AS No Must match
The split horizon rule states: Never advertise a route out of the interface through which you learned it
Poison reverse is another way of avoiding routing loops. Its rule states:
Once you learn of a route through an interface, advertise it as unreachable back through that same interface
EIGRP router uses the RD value when determining if a possible route can be considered to be a loopfree backup route called feasible-successor. It calls these alternative immediately usable loop-free route feasible successor routes because they can feasibly be used as a new successor route when the current successor route fails.
A route determine if a route is a feasible successor based on the feasible condition, if a non-successor route's RD is less then the FD the route is a feasible successor route.
Going Active
When EIGRP removes a successor route and no FS route exist, the route begins a process by which the route discovers if any loop free alternative route reach that prefix. This process is called going active on a route.
Route for which the route has a successor route and no failure has yet occurred remains in a passive state.
Route for which the successor route fails, with no feasible successor routes move to an active state.
- Change state from passive(p) to active(a)
- Query message sent to ever neighbor except the neighbor in the failed route
SIA is for 3 min
R-Query
r- SIA Query
RTO- retransmission timeout
SRTT
If unicast ACKs are not received from a neighbor after the RTO time (Retransmission Time Out), another update message will be sent directly to that neighbor via unicast.
The RTO time is calculated from the SRTT (Smoothed Round Trip Time)
The SRTT is measured by the delay observed between updates and ACKs
Stuck in active:- When a router notice a route failure and moves a route from passive to active state,, that router sends query messages to its neighbor.
The point is that a router may wait while before message before getting reply message in response to each query message for an active route. A router cannot use any alternate paths for that route until all such reply messages have been received.
To deal with this potentially long time, IOS first sets a limit on how long it should take to receive all such replies, that called the active timer is set to 3 min by default.
Routes for which a router does not receive a reply within the active timer are considered to be stuck in active.
SIA query message is sent to each neighbor that has yet to send back a reply. The purpose of the message is meaning that the neighbor really is still waiting for reply to its own query.
Variance lets IOS add EIGRP route considered to be equal routes and may be place into the routing table upto the number of routes defined by the maxium-paths command.
Any FS route whose calculated metric is less than or equal to the product of varience times FD are added to the IP routing table.
AD
Summary 5
Internal 90
External 170
Multicast address 224.0.0.10
Port 88
- Defines same basic topology information about each route for each unique prifix length
- the basic information includes the prefix, prefix length and metric information and few other details. EIGRP neighbors exchange topology information, each router storing the learned topology information in there respective EIGRP topology table.
- to get the process started each EIGRP router needs to add topology data for some prefix so it can then advertise these route to its EIGRP neighbor
- A router EIGRP process adds subnet to its local topology without learning the topology data from an EIGRP neighbor and three sources
- Prefixes of connected subnets for interfaces on which EIGRP has been enabled on that router using network command
- Prefix of connected subnets for interfaces referenced in an EIGRP neighbor command
- Prefix learned by the redistribution of routes into EIGRP from other routing protocols
EIGRP Update Message(HUQRA)
Hello
Update
Query
Reply
Acknowledge(ACK)
Update and ACK are used as two messages as part of the topology data exchange process
Update message contains the topology information whereas ACK receipts of the update packet
Update message contains following information
- Prefix
- Prefix lenght
- Metric components: bandwidth, delay, reliability and load
- Non-metric items: MTU and hop count
default setting for load -1 reliability- 255
EIGRP for delay add the delay value of the interface update received on to the delay value received
for bandwidth EIGRP simply chooses the lowest bandwidth compairing the bandwidth of its own interface with the bandwidth listed in the received EIGRP update.
EIGRP Update Process
- when a neighbor first comes up the router exchange full updates meaning the router exchange all topology information
- after all prefixes have been exchanged with a neighbor the update cease with that neighbor if no change occurs in the network, there is no periodic reflooding of topology data
- if something changes the router sends partial updates about only the prefix whose status or metric component have changed
- if a neighbor fails and then recovers or new neighbor adjacency are formed full update occurs over these adjacency.
- EIGRP uses split horizon rule on most of the interfaces by default
- To send update EIGRP uses the Reliable Transport Protocol(RTP) to send the updates and confirm receipt. The RTP manages the delivery and reception of EIGRP packets. Reliable delivery means that delivery is guaranteed and that packets will be delivered in order. Guaranteed delivery is accomplished by means of algorithm known as reliable multicast, using the reserved class D address 224.0.0.10. Each neighbor receiving a reliably multicast packet unicasts an acknowledgment.
- EIGRP routes must be reachable using layer 2 frames before they can exchange hello messanges and become EIGRP Neighbor.
- EIGRP router builds IP routing table entries by processing the data in the topology table
Metric Calculation
EIGRP topology table entry for a single prefix/lenght list the one or more possible routes, each route list the various component metric value-bandwidth, delay and so on. Additionally for connected subnets the database entry list an outgoing interface.
for route not connected to the local router, in addition to an outgoing interface the database entry also lost the IP address of the EIGRP neighbor that advertise route.
An EIGRP router does its calculation both from its own prospective anf from the prospective of the next hop router of the route.
The two values are called FD and RD
Feasible Distance(FD):- Integer metric for the route from the local perspective, used by the local router to choose the best for the prefix
Reported Distance(RD):- Integer metric for the route from the neighboring router's prospective(the neighbor that told the local router about the route). Used by the local router converging to new routes.
Route use teh FD to determine the best route based on the lowest metric and use the RD when falling back to an alternative route when the best fails.
when a route has calculated the integer FD for each possible route to reach single prefix/length that router can then consider adding the lowest metric route to the IP routing table.
FD- end to end metric
RD- metric reported by neighbor to a particular destination
FC= RD
RD of feasible successor must be less than FD of successor
Slower the bandwidth worst the metric.
Metric= 256x(107/slowest-bw)+cumulative delay)
Tuning Metric
- Setting interface bandwidth
- Setting Interface Delay
- configuring K values
- adding metric in offset-list
bandwidth is in Kb/sec
delay is in 10s of microsecond
EIGRP Wide Metrics
The Enhanced Interior Gateway Routing Protocol (EIGRP) composite cost metric (calculated using the bandwidth, delay, reliability, load, and K values) is not scaled correctly for high-bandwidth interfaces or Ethernet channels, resulting in incorrect or inconsistent routing behavior. The lowest delay that can be configured for an interface is 10 microseconds. As a result, high-speed interfaces, such as 10 Gigabit Ethernet (GE) interfaces, or high-speed interfaces channeled together (GE ether channel) will appear to EIGRP as a single GE interface. This may cause undesirable equal-cost load balancing. To resolve this issue, the EIGRP Wide Metrics feature supports 64-bit metric calculations and Routing Information Base (RIB) scaling that provide the ability to support interfaces (either directly or via channeling techniques like port channels or ether channels) up to approximately 4.2 terabits.
By default, the EIGRP composite cost metric is a 32-bit quantity that is the sum of segment delays and the lowest segment bandwidth (scaled and inverted) for a given route. The formula used to scale and invert the bandwidth value is 107/minimum bandwidth in kilobits per second. However, with the EIGRP Wide Metrics feature, the EIGRP composite cost metric is scaled to include 64-bit metric calculations for EIGRP named mode configurations.Composite Cost Metric = (K1*Minimum Throughput) + (K3*Total Latency)
Minimum Throughput = (107* 65536)/Bw), where 65536 is the wide-scale constant.
Metric weight(K Values) from 0-255
k1 and k3 are 1 by default
EIGRP requires that two routers k-value match before those routers can become neighbor
AS No Must match
The split horizon rule states: Never advertise a route out of the interface through which you learned it
Poison reverse is another way of avoiding routing loops. Its rule states:
Once you learn of a route through an interface, advertise it as unreachable back through that same interface
EIGRP router uses the RD value when determining if a possible route can be considered to be a loopfree backup route called feasible-successor. It calls these alternative immediately usable loop-free route feasible successor routes because they can feasibly be used as a new successor route when the current successor route fails.
A route determine if a route is a feasible successor based on the feasible condition, if a non-successor route's RD is less then the FD the route is a feasible successor route.
Going Active
When EIGRP removes a successor route and no FS route exist, the route begins a process by which the route discovers if any loop free alternative route reach that prefix. This process is called going active on a route.
Route for which the route has a successor route and no failure has yet occurred remains in a passive state.
Route for which the successor route fails, with no feasible successor routes move to an active state.
- Change state from passive(p) to active(a)
- Query message sent to ever neighbor except the neighbor in the failed route
SIA is for 3 min
R-Query
r- SIA Query
RTO- retransmission timeout
SRTT
If unicast ACKs are not received from a neighbor after the RTO time (Retransmission Time Out), another update message will be sent directly to that neighbor via unicast.
The RTO time is calculated from the SRTT (Smoothed Round Trip Time)
The SRTT is measured by the delay observed between updates and ACKs
- Smooth round-trip time (SRTT)—The number of milliseconds it takes for an EIGRP packet to be sent to this neighbor and for the local router to receive an acknowledgment of that packet
- Retransmission timeout (RTO), in milliseconds—The amount of time that the software waits before retransmitting a packet from the retransmission queue to a neighbor
- Q count—The number of EIGRP packets (Update, Query, and Reply) that the software is waiting to send
- Unidirectional link
- Uncommon subnet, primary, and secondary address mismatch
- Mismatched masks
- K value mismatches
- Mismatched AS numbers
- Stuck in active
- Layer 2 problem
- Access list denying multicast packets
- Manual change (summary router, metric change, route filter)
Stuck in active:- When a router notice a route failure and moves a route from passive to active state,, that router sends query messages to its neighbor.
The point is that a router may wait while before message before getting reply message in response to each query message for an active route. A router cannot use any alternate paths for that route until all such reply messages have been received.
To deal with this potentially long time, IOS first sets a limit on how long it should take to receive all such replies, that called the active timer is set to 3 min by default.
Routes for which a router does not receive a reply within the active timer are considered to be stuck in active.
SIA query message is sent to each neighbor that has yet to send back a reply. The purpose of the message is meaning that the neighbor really is still waiting for reply to its own query.
Variance lets IOS add EIGRP route considered to be equal routes and may be place into the routing table upto the number of routes defined by the maxium-paths command.
Any FS route whose calculated metric is less than or equal to the product of varience times FD are added to the IP routing table.
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