what is difference between designated router and backup
designated router and explain feature of both router.
Answers were Sorted based on User's Feedback
Answer / jitu
A designated router (DR) is the router interface elected
among all routers on a particular multiaccess network
segment, generally assumed to be broadcast multiaccess.
Special techniques, often vendor-dependent, may be needed to
support the DR function on nonbroadcast multiaccess (NBMA)
media. It is usually wise to configure the individual
virtual circuits of a NBMA subnet as individual
point-to-point lines; the techniques used are
Do not confuse the DR with an OSPF router type. A given
physical router can have some interfaces that are designated
(DR), others that are backup designated (BDR), and others
that are non-designated. If no router is DR or BDR on a
given subnet, the DR is first elected, and then a second
election is held if there is more than one BDR.  The DR
is elected based on the following default criteria:
* If the priority setting on a OSPF router is set to 0,
that means it can NEVER become a DR or BDR (Backup
* When a DR fails and the BDR takes over, there is
another election to see who becomes the replacement BDR.
* The router sending the Hello packets with the highest
priority wins the election.
* If two or more routers tie with the highest priority
setting, the router sending the Hello with the highest RID
(Router ID) wins. NOTE: a RID is the highest logical
(loopback) IP address configured on a router, if no
logical/loopback IP address is set then the Router uses the
highest IP address configured on its active interfaces.
(e.g. 192.168.0.1 would be higher than 10.1.1.2).
* Usually the router with the second highest priority
number becomes the BDR.
* The priority values range between 0 - 255, with a
higher value increasing its chances of becoming DR or BDR.
* IF a HIGHER priority OSPF router comes online AFTER
the election has taken place, it will not become DR or BDR
until (at least) the DR and BDR fail.
* If the current DR 'goes down' the current BDR becomes
the new DR and a new election takes place to find another
BDR. If the new DR then 'goes down' and the original DR is
now available, it then becomes DR again, but no change is
made to the current BDR.
DR's exist for the purpose of reducing network traffic by
providing a source for routing updates, the DR maintains a
complete topology table of the network and sends the updates
to the other routers via multicast. All routers in an area
will form a slave/master relationship with the DR. They will
form adjacencies with the DR and BDR only. Every time a
router sends an update, it sends it to the DR and BDR on the
multicast address 220.127.116.11. The DR will then send the
update out to all other routers in the area, to the
multicast address 18.104.22.168. This way all the routers do not
have to constantly update each other, and can rather get all
their updates from a single source. The use of multicasting
further reduces the network load. DRs and BDRs are always
setup/elected on Broadcast networks (Ethernet). DR's can
also be elected on NBMA (Non-Broadcast Multi-Access)
networks such as Frame Relay or ATM. DRs or BDRs are not
elected on point-to-point links (such as a point-to-point
WAN connection) because the two routers on either sides of
the link must become fully adjacent and the bandwidth
between them cannot be further optimize
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Answer / chetan shende
DR sends heart beats to other routers and updates in their routing tables BDR keep backup of routing table of DR in case of DR failure BDR elected as DR.
|Is This Answer Correct ?||6 Yes||0 No|
Answer / karthik
DR and Bdr concept work in broadcat multi access network.
It reduces Lsa floodind within broadcast domain by electing
one DR and Bdr to which other routers in broadcast domain
form adjacency. So that only Dr and BDR have full adjacency
that means full link state database.
any change in broadcast domain will be send as link state
update to the Dr from which it will be forwarded to other
members reducing Lsa transfer
|Is This Answer Correct ?||4 Yes||0 No|
Answer / jitendera
the above answer is taken from google so it might be
possible that some of my friend are not going to undersatnd
the consept of dr and bdr
note-plase donot confuse betwwenrouter type in ospf that is
abr and asbr etc
not let suppose that there are three router concted through
the swithch that is called ospf over broadcastas we know
that switch is a multiassess device taht is any cahnge
happen betwen the n/w te router cahnge the updates and this
will cause hevay tarfic jam accros thenetwork to avoid this
dr nad bdr consepts comes
dr that is best router interface
bdr-2nd best router (for backup)
for dr and bdr some ip is reserved that is 22.214.171.124
slection criterai of dr and bdr
1 ip nad mask
2 port pirorty
rest of anser is writen above i have tried to make it soo simple
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Answer / guest
desigmated router is stor router. it can store all data &
backup desigmated router working on loss data
|Is This Answer Correct ?||0 Yes||4 No|
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