Does Router Broadcast?

Replies

• 

  Ankita Katdare

  #-Link-Snipped-# Check if this #-Link-Snipped-# helps.
• 

  durga ch

  when u say broadcast> is it l2 broadcast or l3 broadcast? please be more specific on your question.as well just to add up? are you refering to l3 control packets or data packets?
• 

  pawanpreet singh

  I wanna know about both L2 and L3 broadcast .. plz give me full description about it ..
• 

  pawanpreet singh

  pawanpreet singh

  I wanna know about both L2 and L3 broadcast .. plz give me full description about it ..

• 

  Ankita Katdare

  I think these lecture notes would help - #-Link-Snipped-#
  
  From what I know, there are two broadcast addresses one for each layer:
  1. At layer 2 there is a broadcast address for MAC address which is always FF:FF:FF:FF:FF:FF.
  2. At layer 3 there is a broadcast address for the IP address. This is not independent and is related to the mask value associated.
  
  Correct me if I am wrong.
• 

  durga ch

  Hi pawan,
  
  Simplest exmaple possible is as below
  L2 broadcasts are generally done when the mac address of a specific device is unknown.
  For example, in your given LAN you put a new switch and the switchs ARp table is currently empty . In this case, consider system A sends a packet to system B in same LAN, the switch does a source based mac address learning for A, but it is still unaware of location of B. That is when it sends out an Broadcast ARP message asking for a MAC ID associated with specific Ip address.
  I am not sure (at least till today) if routers actually do a broadcast at control plane. They really dont have to. Take this example-
  If the Ip address in my paket is available, then the router forwards the packet to the destination. If the Ip address is not available , it either drops the packet or sends it to default gateway based on other criteria as whether classful/classless ip scheme is used and whether a default gateway is considered so on...
  Yes, routers do a limited broadcast known as multicasting, where they send packets to multiple hosts at once. For example - Routers mutlicast routing updates for address like 225.0.0.9/10 for eigrp.
• 

  pawanpreet singh

  durga thnx for telling me ..
  
  Pc .......>S1......>R1......>DHCP Server ..
  
  Now tel me if PC needs an IP address and it broadcasts ..
  Will router forward it to DHCP server or not ?
• 

  durga ch

  😀. cisco has this configuration command 'ip helper address'.
  Whenever the PC sends a DHCP request, the router simply drops it. But when 'ip helper address x.x.x.x' is configured on the inbound interface of the R1 router , the packets are sent as unicast address for the specific x.x.x.x address/ in this case the DHCP server ip.
  
  hope that answers your query
• 

  pawanpreet singh

  thnx durga for resolving my queries ..
• 

  vishakkv

  no router stops broadcasting.
• 

  durga ch

  #-Link-Snipped-# - does your statement "no router stops broadcastin " means "all routers broadcast" or
  it means - "no, routers stop broadcast"
  
  please clarify and justify
• 

  pawanpreet singh

  I wanna ask one thing ..
  When we use SSH instead of telnet in switch then why do we need domain name command for configuring SSH .. I couldn't get " ip domain-name " command ..
  Plz clearify it ..
• 

  durga ch

  the ssh token is combination of the domain name hostname and rsa. I will get back to you on this.