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VLAN - ARP strange

Dawid Chrzan
Occasional Contributor

VLAN - ARP strange

I have 2 switches
7710 - on port 1 i have 3 vlans - vlan10 untagged , vlan20 tagged ,
vlan30 tagged.
port 8 uplink to second switch 7841 - tagged - also 3 vlans as above

7841 - i have 3 vlans
port 24 uplink tagged to switch 7710.
port 1 untagged traffic from vlan10
port 10 - tagged trafic vlan20 and vlan30

Everything works fine - more less - but i am curious about ARP.


When 10.0.20.10 (untagged win xp connected to port 1 on on 7710 switch) pings 10.0.20.11 ( linux tagged vlan20 vid20 - connected to port 10 on 7841 switch ) - there is no chance for communication - and this is OK.
But i see on eth1 of this box (10.0.20.11) ARP packets.

3. 080000 00:15:17:26:1c:fe > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
length 42: arp who-has 10.0.20.10 tell 10.0.20.11
1. 000001 00:15:17:26:1c:fe > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
length 42: arp who-has 10.0.20.10 tell 10.0.20.11
999999 00:15:17:26:1c:fe > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length
42: arp who-has 10.0.20.10 tell 10.0.20.11
3. 496000 00:15:17:26:1c:fe > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
length 42: arp who-has 10.0.20.10 tell 10.0.20.11
1. 000000 00:15:17:26:1c:fe > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
length 42: arp who-has 10.0.20.10 tell 10.0.20.11
1. 000001 00:15:17:26:1c:fe > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
length 42: arp who-has 10.0.20.10 tell 10.0.20.11


Why eth1 in vlan20 connected to port tagged trunk in vlan20 asks for MAC of station connected to some other vlan?

Is it normal and OK ?

Even if remove port 24 from vlan20 i still see arp who has.
Bug in switch firmware ? ( Thanks God it is not HP switch ) :)

Configuration of both switches.

o65-7710
------

p8 pvid10 tagged vid10 vid20 vid30 - uplink

p1 vid10 untagged pvid10 , vid20 tagged , vid30 tagged

Name :test20
VID :20
Member:1 2 3 4 5 6 7 8
Untag :
Name :test10
VID :10
Member:1 2 3 4 5 6 7 8
Untag :1 2 3 4 5 6 7
Name :test30
VID :30
Member:1 2 3 4 5 6 7 8
Untag :


065-7841
-------
p24 trunk tagged vid10 vid20 vid30 - uplink

p01 acces vid10 untagged

p10 trunk tagged vid20 vid30


Vlan Name : test10
Vlan ID : 10
IGMP Aware : disable
Private VLAN : enable
GVRP Propagation : disable
Member : 1 24

Vlan Name : test20
Vlan ID : 20
IGMP Aware : disable
Private VLAN : enable
GVRP Propagation : disable
Member : 10 24

Vlan Name : test30
Vlan ID : 30
IGMP Aware : disable
Private VLAN : enable
GVRP Propagation : disable
Member : 10 24

Thanks for any suggestions and help.

Dawid Chrzan