How IP addresses work on Layer 2 switches ?

[abhdivak]

Hello All,

How IP addresses work on Layer 2 switches and In real time, how we are monitoring L2 switches ?

Thanks,

Abhijith

[Joseph W. Doherty · Accepted solution]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

On a pure L2 unmanaged switch, there's no IP addresses.  On a pure L2 managed switch, the switch operates as most other IP hosts, i.e. it has an IP for management purposes, which often also allows for monitoring its via SNMP (or other).

[abhdivak]

Hello Joseph,

In real time then how will we monitor unmanaged L2 switch, if its goes down how will we come to know ?

Regards,

Abhijith

[Karsten Iwen]

There are typically two trigger conditions in that case:

1. You monitor devices that are connected to that unmanaged switch
2. The users will call you ;-)

[abhdivak]

Hello Karsten,

What is the use of SVIs in L2 managed switch ? If a L2 switch is not able to read L3 information , how its works ?

Regards, Abhijith

[Ganesh Hariharan]

Hello Karsten,What is the use of SVIs in L2 managed switch ? If a L2 switch is not able to read L3 information , how its works ? Regards, Abhijith

Hello Abhijith,

SVI in L2 managed devices is for management purpose of that device, which can be used for SNMP polling with your monitoring devices and for doing admin configuration task in that L2 managed devices.

Hope it Helps..

-GI

[abhdivak]

Hi,

Let me understand deeply, assume i connect a L2 switch and router and created a SVI on switch with ip add 10.1.1.1/24 and 10.1.1.2/24 on router side. If i ping 10.1.1.1 from router, how packets flows ? Let me try explain, For ping, the protocol work behind is ICMP and for ICMP echo request, its needs destination mac and for that arp request will send directly as the destination belongs to same subnet. Once the switch got the arp request it can process layer 2 information only right ? If it cannot ready L3 info, how will it give arp reply ? ( I mean switch need to know destination ip address)

Regards,

Abhijith

[Karsten Iwen]

As Joseph already mentioned, the IP-logic of the switch has to be thought of like a host that is connected to an internal port of the switch. This "host" is completely aware of his own IP- and MAC address and can answer to arp-requests (and much more).

[abhdivak]

Hello Karsten,

That means once we create SVI on a L2 switch, if that switch receives a arp broadcast and it will also do a broadcast to find out the destination and the SVI give a replay. Right ?

Thanks,
Abhijith

[Karsten Iwen]

You have to be aware that the Term "Layer 2 switch" only means that the forwarding of packets is done based on L2 information (this is the data-plane). Nothing more! In addition to that there can be many features that look at higher layers like the mentioned Management. Another feature that is also available on L2 switches is for example DHCP-snooping which even inspects the L7 protocol of the packet. These functions work in the control- or management-plane.

[Ganesh Hariharan]

Hi Abhijith, Agree with karsten, As you know it is unmanaged devices so either any device which is connected should be in managed state and that port is under monitoring which is connected with unmanned device for any proactive alert. Hope it Helps.. -GI