Cisco Packet Tracer, why everytime i send PDU from PC1 to Router 3, the switch will always broadcasting frame? Even switch already know the destination mac address

[Georg Pauwen]

Hello,

not really sure what you are asking...can you elaborate ?

By default, a switch will send traffic to all ports in the broadcast domain...is this what you are referring to ?

[Thomas Leong]

Hi Georg,

I actually learning with First Hop Redundancy Protocol

Lets said my pc1 send pdu to router 3, assume that switch does not know what is the destination (Router 3) mac address is, so the switch will broadcasting frame to look for destination (Router 3)mac address. once switch know the router 3 mac address, switch will save the router 3 mac address into mac address table.

by right once the switch know the destination of the mac address, it does not need to broadcasting frame again right?

Sorry for my bad english, hopefully u can understand haha~ thanks

Maybe u can take a look for my packet tracer file

[Martin L]

Yes, 1st ping packets should be B-cast by switch but not the second one. something does not look right for PT with HSRP. It could be PT fault.

PC sends ARP frame to solve IP to MAC addressing; then at Switch, if destination MAC is not in table, switch does B-cast of that frame. 2nd ping to same destination should be fine since MAC should be saved in switch MAC table by switch.

I will check your PT file later.

Regards, ML
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[Thomas Leong]

Hey Martin,

Thanks for your reply and help.

Regards,

Thomas

[Martin L]

Your design looks weird; not sure if it bad, just looks not traditional (may work on real gear).  Usually 2 HSRP routers would have duplicate/redundant connections to other switches and connection between them.

Or your L2 switch0(1) and switch1(1) would be L3 and doing HSRP.  No HSRP on routers, just on 2 middle switches (next to them) after conversion to L3 switches.

You can see samples of HSRP made by PT if you open PT Samples under File >samples>router>hsrp

older exam book for CCNP Switch exam have some examples, let me know if you want me post 1 or 2 pics.

Regards, ML
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[Thomas Leong]

Hi Martin L,

im playing with HSRP Load Balancing (Not Fully Load Balancing)

Lets assume that both Routers is ISP 1 and ISP 2

So i want VLAN10 go ISP 2, then VLAN20 go ISP 1.

Lets assume that the Switch 0 fa0/4 is down, VlAN20 is not able go ISP 1, so VLAN20 will go ISP 2

Thanks,

Thomas

[Thomas Leong]

Hi Martin,

Yeah u can send me some CCNP older exam example picture for me to see and learn

im still learning with my CCNA haha

Thanks,

Thomas

[Martin L · Accepted solution]

Your requirement for fail-over to ISP 1 from ISP2 if x is down is not directly related to NHRP. That would be something tied to PBR, policy-based routing, a CCNP Route topic.

HSRP meant to be for LAN devices (end-devices) to reach its default gateway (still your routers), aka redundancy at LAN area of network.  Then, we move to ISP fail-over if you have 2 ISPs.  your option for that would more likely involved BGP and PBR.  That is independent of FHRPs at LAN.

I recommend use GNS3 with real IOS image for PBR, HSRP, and possible BGP for fail-over ISP simulation.

Regards, ML
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[Martin L · Accepted solution]

This option of using HSRP on L3 switches (middle ones but those could be replaced by 2 routers) is most common shown in the design books

[Thomas Leong]

Hi Martin L,

Thanks for your help (Thumb up!!), i will try it out later

[Martin L]

Yes, it seems that PT supports HSRP on those L3 switches; it takes standby commands. but I have not tried yest.

Open PT samples to check configs first, then re-do your own lab.

Good luck!

Regards, ML
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