1. Characteristics of Routing Protocols Flashcards
The amount of time for routes to failover is called what?
Convergence time
A routing protocol that exchanges routes between routers in a single AS is known as what type of routing protocol?
IGP (interior gateway protocol)
A routing protocol that exchanges routes between routers in a different AS is known as what type of routing protocol?
EGP (exterior gateway protocol)
Note: there used to be a protocol called EGP
What are the 3 types of routing protocols based on the way they receive, advertise, and store routing info?
Distance-vector
Link-state
Path-vector
How does a distance-vector routing protocol send routing updates?
Periodically send the full copy of its routing table even if there have been no changes.
Distance-vector routing protocols typically use one of two approaches for preventing routing loops. What are they?
Split Horizon
Poison Reverse
How does Split Horizon prevent routing loops?
It prevents a route learned on one interface from being advertised back out of that same interface.
How does Poison Reverse prevent routing loops?
It causes a route received on one interface to be advertised back out of that same interface with a metric considered to be infinite.
Name two distance-vector routing protocols.
RIP
EIGRP
EIGRP is know termed as an advanced distance-protocol because of enhancements. How did EIGRP improve routing advertisement?
It does not periodically send out its entire IP routing table to its neighbors. Instead it uses triggered updates, and it converges quickly.
How does a link-state routing protocol send routing updates?
Routers send link-state advertisements (LSA) to advertise the networks they know how to reach. They send the full list only the first time and then only update the changes when they occur.
Name the two link-state routing protocols.
Open Shortest Path First (OSPF)
Intermediate System–to–Intermediate System (IS-IS)
What is the algorithm used by OSPF and IS-IS?
Dijkstra’s Shortest Path First
BGP is the only EGP protocol really used today. What is the enhanced version that supports IPv6 called?
Multiprotocol BGP (MP-BGP)
What does NBMA stand for?
Nonbroadcast multiaccess
What IPv4 traffic type does not exist in IPv6?
Broadcast
What does an IPv6 global unicat address begin with?
2000::/3
What address class is an IPv4 multicast?
Class D
In IPv6 networks, multicast addresses have a prefix of what?
ff00::/8
One-to-nearest describes what type of IPv6 traffic?
Anycast
What is the calculation for bandwidth-delay product?
It is calculated by multiplying the segment’s bandwidth
in bits/sec) by the latency packets experience as they cross the segment (in sec
What is an ICMP Destination Unreachable message?
If a packet enters a router destined for an address that the router does not know how to reach, the router can let the sender know by sending a Destination Unreachable ICMP message back to the sender.
What is an ICMP Redirect message?
A host might have routing information indicating that to reach a particular destination network, packets should be sent to a certain next-hop IP address. However, if network conditions change and a different next-hop IP address should be used, the original next-hop router can let the host know to use a different path by sending the host a Redirect ICMP message.
What are the steps in the TCP three-way handshake?
Initiator sends SYN
Target send ACK plus SYN
Initiator send ACK
What does the MSS stand for in TCP MSS?
Maximum Segment Size
Does the segment size limited by TCP MSS include any headers?
No
What is TCP windowing?
TCP will increase the number of segments sent without expecting an ACK. It will start with one segment and double the number of segments until drops happen.
With TCP windowing, what happens when packets are dropped (and what is this called)?
TCP will go back to sending a single segment and doubling each time until it reaches half the number when the drop occurred.
Called TCP slow start.
What is global synchronization?
A router’s queue gets filled and packets from multiple flows gets dropped causing TCP slow start on all those flows.
What feature does Cisco support to help prevent global synchronization?
Weighted Random Early Detection (WRED), which can pseudo-randomly drop packets from flows based on the number of packets currently in a queue and the quality of service (QoS) markings on the packets. By dropping packets before the queue fills to capacity, the global
synchronization issue is avoided.
What is LLQ and what does it do?
Low Latency Queuing allows one or more traffic types to be buffered in a priority queue, which is serviced first.
