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  • Does Router Broadcast?

    pawanpreet singh

    Member

    Updated: Oct 25, 2024
    Views: 946
    Can someone inform me the basics of router and how does a router brodcast signal, if it actually does?
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Replies

  • Ankita Katdare

    Administrator • Jun 17, 2012

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

    Member • Jun 17, 2012

    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?
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  • pawanpreet singh

    Member • Jun 17, 2012

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

    Member • Jun 18, 2012

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

    Administrator • Jun 18, 2012

    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.
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  • durga ch

    Member • Jun 18, 2012

    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.
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  • pawanpreet singh

    Member • Jun 18, 2012

    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 ?
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  • durga ch

    Member • Jun 19, 2012

    😀. 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
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  • pawanpreet singh

    Member • Jun 21, 2012

    thnx durga for resolving my queries ..
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  • vishakkv

    Member • Jun 21, 2012

    no router stops broadcasting.
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  • durga ch

    Member • Jun 21, 2012

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

    please clarify and justify
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  • pawanpreet singh

    Member • Jun 22, 2012

    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 ..
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  • durga ch

    Member • Jun 22, 2012

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