16.0 HSRP:
HSRP stands for Hot Standby Routing Protocol. The following are
members of HSRP group:
1. Virtual router: virtual router is what
is seen by the end user device. The virtual router has its own IP
and MAC addresses.
2. Active router: Forwards packets sent to
the virtual router. An active router assumes the IP and MAC addresses
of the virtual router.
3. Standby router: Standby router monitors
the state of HSRP by using Hello massages. It assumes the role of
Active router, should the current Active router fail.
Image router
does not exist and is not a part of HSRP group.
When an Active router fails in HSRP environment, Standby router
assumes the Active router role. This new Active router will remain
as Active router even if the failed Active router comeback to service,
irrespective of the priority levels.
To enable the previous Active
router to resume its activity as Active router by taking over the
role from a lower priority Active router, use the command:
Rtr(config-if)#
standby <group-number> preempt
The hosts served by HSRP router use the IT address of virtual router as the default IP address.
Each router in a standby group can be assigned a priority value.
The range of priority values is between 0 and 255 (including 0 and
255). The default priority assigned to a router in a standby group
is 100. The router with numerically higher priority value will become
Active router in the HSRP standby group.
The command used to
set the router's priority in standby group is:
R(config-if)#
standby <group-number> priority <priority-value>.
17.0 Multicasting:
17.1 The following are some of the characteristics of IP multicast traffic:
1. IP multicast traffic uses Class D range of addresses from
224.0.0.0 to 239.255.255.255.
2. A Class D address consists of
1110 as the higher-order bits in the first octet.
3. Multicast
packets use User Datagram Protocol. UDP is considered unreliable,
because UDP does not support flow control, error recovery functions.
4. 224.0.0.1 represents all hosts on a subnet; 224.0.0.2 represents
all routers on a subnet.
5. The addresses in the range 224.0.0.0 - 224.0.0.255 are reserved
for use by network protocols on a local network segment. Packets
with these addresses should never be forwarded by a router. The
time-to-live (TTL) for these packets is always set to a value 1
by the originating router, so that these packets never cross local
segment.
6. The address range 239.0.0.0 - 239.255.255.255 are
called Administratively Scoped Addresses and analogous to private
addresses 10.0.0.0/8.
17.2 Mapping IP Multicast to a MAC address:
The high order
9 bits (out of total of 32 bits) of the IP address are not used
for mapping into the MAC address. The lower 23 bits are mapped to
lower 23 bits of MAC address.
For example, take a Multicast address:
224.12.9.4. Convert to binary equivalent:
224.12.9.4 = 1110.0000.0000.1100.0000.1001.0000.0100
Take only the last 23 bits = 000.1100.0000.1001.0000.0100 = 0c-09-04
Append the Ethernet Multicast address: 01-00-5E. Note that 01-00-5E
always precedes a Multicast MAC address. The bit following this
is always a zero.
Therefore, Multicast MAC address for IP address
224.12.9.4 is:
01-00-5E-0C-09-04.
18.0 Unicast Traffic:
The following are true about Unicast traffic:
1. The number
of times a packet is transmitted is proportional to the number of
hosts that need to receive the packet. If there are N number of
hosts that need to receive a packet, the packet is transmitted N
times over the network. This increases the Bandwidth consumption
and resource consumption on the network.
2. All Unicast traffic
need to know the destination address, whereas, Multicast and broadcast
messages need not know the destination addresses.
3. Unicasting
can work with both TCP and UDP protocols.
19.0 Dense Mode Routing Protocols:
Dense mode routing protocols are suited when all or most of the
routers in a network need to distribute multicast traffic.
Some
examples of Dense Mode Routing Protocols are:
1. Distance Vector
Multicast Routing Protocol (DVMRP)
2. Multicast Open Shortest
Path First (MOSPF)
3. Protocol Independent Multicast Dense Mode
(PIM DM)
20.0 Sparse Mode Routing Protocols:
Sparse mode routing is suitable when there the Multicast group
members are sparsely distributed. These protocols put less strain
on network bandwidth, compared to Dense mode protocols.
Some
examples of Sparse Mode Routing Protocols:
1. Core-Based Trees
(CBT)
2. Protocol Independent Multicast Sparse Mode (PIM SM)
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