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Why do broadcasts fail to reach hosts in wlan only when BVI has an ip?

fullaccess
Level 1
Level 1

I have the following network (see attachment):

fullaccess_0-1698685572245.png

Router's interfaces:

Interface                      IP-Address OK? Method Status                         Protocol

GigabitEthernet0          unassigned YES NVRAM  administratively down down

FastEthernet0               unassigned YES unset     up                              up

FastEthernet1               unassigned YES unset     up                              up

FastEthernet2               unassigned YES unset     up                              down

FastEthernet3               unassigned YES unset     up                              down

Serial0                          unassigned YES NVRAM administratively down down

Wlan-GigabitEthernet0 unassigned YES unset     up                              up

wlan-ap0                     192.168.0.1 YES TFTP    up                              up

Cellular0                       unassigned YES IPCP     administratively down down

Vlan1                           192.168.0.1 YES manual up                              up

 

embedded AP's interfaces:

Interface             IP-Address OK? Method Status                       Protocol

GigabitEthernet0 unassigned YES NVRAM up                             up

Dot11Radio0      unassigned YES NVRAM up                             up

Dot11Radio1      unassigned YES NVRAM administratively down down

BVI1                  192.168.0.2 YES manual up                              up

 

AP's gig0 and dot11radio0 are in the same bridge group.

 

When I ping 192.168.0.255 from a pc I get a response from all wired hosts, wlan's hosts and AP's BVI1 dont respond. When I ping from a laptop, I only get a response from BVI1. Why is that? Arent all hosts on the same vlan? Isnt there a bridge forwarding all frames from the lan to the wlan and vice versa?

Edit:

After restarting PT and trying again I found that the ping fails as long as BVI1 has an ip. When BVI1 has no ip, the broadcast reaches all host, but the moment BVI1 gets its ip the ping stops working as it should. I also found that changes to the BVI1 ip do not persist after reload (I made sure to use write memory), so I am forced to get the ip though dhcp. I've updated the attachment.

Edit 2:

After following the packets using simulation mode, I found what goes wrong. When AP's gig0 receives the ICMP request, it immediately constructs a reply and tries to send it to the source IP (it does not forward the request to the dot11radio0 interface, thats why wlan hosts dont respond). Because it doesnt have the source's MAC it constructs a ARP request, but instead of sending it back through gig0 it forwards it to dot11radio0. So only the wlan hosts receive the ARP for the MAC of a wired host, and of course they dont respond. Is this behavior result of a misconfiguration or misunderstanding of bridges on my part? Or is it a PT bug?

 

5 Replies 5

Joseph W. Doherty
Hall of Fame
Hall of Fame

Possibly because WLANs don't use the same broadcast rules as wired LANs.

Martin L
VIP
VIP

I think it's working; PT can get stuck sometimes; Re-open your lab or get one u just shared here and open it.

MartinL_0-1698696524841.png

 

Ah, good reminder about PT can be "quirky".

I.e. whatever PT results, remember they can be incorrect.

After trying again I found more weird behavior. If I try to manually set BVI1 ip address the configuration is lost on reload (even after write memory), I am forced to get an ip through dhcp. Even weirder, the moment BVI1 get's its ip through dhcp pings to 192.168.0.255 stop reaching wlan hosts. Could this be a glitch of PT? I cant find a reason that would explain the network breaking simply because BVI1 has an ip. I've updated my post with a new attachment.

 

 

nothing like that here; PT works fine on Windows; There are several posts about PT problems on MACs and Ubuntu; Search here also see CLN https://learningnetwork.cisco.com/s/discussions

Regards, ML
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