Author: renjithbs

The Open Shortest Path First (OSPF) is an Interior Gateway Protocol used to distribute routing information within a single Autonomous System.

• It is open standard (RFC2328)
• It is a Link-state protocol
• Administrative Distance is 110
• Uses cost as metric
• Fast convergence
• VLSM support
• Scalable to large networks
• Stub capabilities
• Authentication (None, Clear-text, MD5)
• Reliability (Sends only hello messages to maintain neighbour relationship)
• Route tagging capabilities
• Uses multicast for routing updates.

Multicast address used by all                      224.0.0.5

Multicast address used by DR/BDR          224.0.0.6

Timer Intervals

These are the values of the OSPF timers:

• Hello—Interval time in seconds that a router sends an OSPF hello packet.
• Dead—Time in seconds to wait before declaring a neighbour dead. By default, the dead timer interval is four times the hello timer interval.
• Wait—Timer interval that causes the interface to exit out of the wait period and select a DR on the network. This timer is always equal to the dead timer interval.
• Retransmit—Time to wait before retransmitting a database description (DBD) packet when it has not been acknowledged.

Default Timers:

On Broadcast and P2P links

• Hello 10 seconds
• Dead 40 seconds

On NBMA links

• Hello 30 seconds
• Dead 120 seconds

• Neighbour table
• Topology table (all possible paths to the destination)
• Routing Table (Best path)
• Advertised distance (distance between the local router and the next-hop router)
• Feasible distance (sum of these ADs costs is referred to as the feasible distance (FD)
• Successor (Installed in the routing table)

• EIGRP is a Cisco proprietary protocol.
• It has two AD values (Internal – 90, External – 170 )
• Fast Convergence.
• Uses Dual (Diffusing update algorithm).
• No periodic Updates only triggered updates.
• Triggered updates only changes occurred.
• Consumes less bandwidth.
• Multiple network layer support (IPV4, IPV6).
• Use of multicast (224.0.0.10) and unicast.
• Variable-length subnet masking (VLSM) support.
• Composite metric.
• Unequal load balancing (improve use of traffic).
• Protocols number is 88.
• Summarization can be enable in any interface. (Reduce the size of the routing table).
• Uses Hello packets to ensure the neighbour is still alive.
• Reliable Transport Protocol (RTP) responsible for guarantee the EIGRP packets delivery to all neighbors.

Update: frequency of updates, default 30 seconds.

Invalid: seconds since a valid update was seen, to consider the route invalid and placing the route into hold down, default is 180 seconds, in other words six updates. After 180 seconds the route is considered invalid – unreachable (metric is 16).

Hold Down: Once in hold down, how long (in seconds) to “not believe” any equal or less impressive (worse) route updates for routes that are in hold down, default is 180 seconds.

Flush: how many seconds, since the last valid update, until we throw that route in the trash (garbage collection for un-loved non-updated routes)

Defaults are(in seconds), here is what ciscopress says:Update: 30 Invalid: 180 Hold Down: 180 Flush: 240

The Invalid and Holddown Timers start together and have the same default value, what it means is, if a router does not receive any update for 180 seconds – it is considered invalid and during the same time (at least during the wait for an update) the holddown timers is also ticking and will not accept a worse update. The Flush Timers (after 180 seconds) will allow the better metric route to get entered during last 60 seconds and after waiting for 240 seconds since the last update, the route will be flushed from the route table.

Features of RIPv1
It is a universal protocol.
Administrative Distance is 120.
Hop count is used as the metric for path selection.
The maximum hop count is 15, so it supports maximum 16 routers per interface.
Routing updates are broadcast every 30 seconds by default. Because it is a distance vector routing protocol, updates are sent even if no change has occurred.
It uses Bellman ford algorithm for path selection.
RIP can load balance over as many as 16 equal-cost paths (4 paths by default).
It has no authentication support.

It has two versions

RIPv1 is a classful distance vector routing protocol described in RFC 1058 that does not send the subnet mask in its updates.Therefore, RIPv1 does not support VLSM or discontiguous subnets. RIPv1 automatically summarizes at the network boundary and cannot be configured not to.

RIPv2 is a classless distance vector routing protocol defined in RFC 1721, RIP Version 2 Protocol Analysis; RFC 1722, RIP Version 2 Protocol Applicability Statement; and RFC 2453, RIP Version 2. The most significant addition to RIPv2 is the inclusion of the mask in the RIPv2 routing update packet, allowing RIPv2 to support VLSM and discontiguous subnets. RIPv2 automatically summarizes routes on classful network boundaries. As described earlier, however, you can disable this behavior. In addition, RIPv2 uses multicast addressing for more-efficient periodic updating on each interface. RIPv2 uses the 224.0.0.9 multicast address to advertise to other RIPv2 routers. This approach is more efficient than RIPv1’s approach. RIPv1 uses a 255.255.255.255 broadcast address, so all devices, including PCs and servers, must process the update packet. They perform the checksum on the Layer 2 packet and pass it up their IP stack. IP sends the packet to the User Datagram Protocol (UDP) process, and UDP checks to see whether RIP port 520 is available. Most PCs and servers do not have any process running on this port and discard the packet.