06-28-2014
VLANs and their domains
Hey everyone. I work in a data center, and I'm working on getting my CCNA. Now when I read articles on the idea of VLAN's it makes sense. Especially if you have multiple switches daisy chained in multiple locations. My two main questions though are that most of these examples use PC's as examples for using VLAN's. But in the environment I work in, we have clients who have 2 and 3u servers, with multiple hard drive bays in these vlans. I don't know what these machines are running, but what could they possibly need to communicate to each other for?
Even in regards to normal PC's like in the examples I read in the cisco book, what protocol or data is sent directly to another PC? If I'm using something like yahoo instant messenger, and I send a message to the person on the same VLAN, does that packet/frame ever leave the vlan? or is it send directly to the switch and the switch sends it to the receiver? Wouldn't something like that go to a Yahoo messaging server somewhere and then send back to the person sitting next to me?
I ask this because I can't think of information that is send directly from one computer to the next without it ever leaving a vlan. Except transfers files or something and the idea of separating broadcasts.
Hope this line of questioning makes sense! Thanks!
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VLAN manipulation action in tc(8) Linux VLAN manipulation action in tc(8)
NAME
vlan - vlan manipulation module
SYNOPSIS
tc ... action vlan { pop | PUSH | MODIFY } [ CONTROL ]
PUSH := push [ protocol VLANPROTO ] [ priority VLANPRIO ] id VLANID
MODIFY := modify [ protocol VLANPROTO ] [ priority VLANPRIO ] id VLANID
CONTROL := { reclassify | pipe | drop | continue | pass | goto chain CHAIN_INDEX }
DESCRIPTION
The vlan action allows to perform 802.1Q en- or decapsulation on a packet, reflected by the operation modes POP, PUSH and MODIFY. The POP
mode is simple, as no further information is required to just drop the outer-most VLAN encapsulation. The PUSH and MODIFY modes require at
least a VLANID and allow to optionally choose the VLANPROTO to use.
OPTIONS
pop Decapsulation mode, no further arguments allowed.
push Encapsulation mode. Requires at least id option.
modify Replace mode. Existing 802.1Q tag is replaced. Requires at least id option.
id VLANID
Specify the VLAN ID to encapsulate into. VLANID is an unsigned 16bit integer, the format is detected automatically (e.g. prefix
with '0x' for hexadecimal interpretation, etc.).
protocol VLANPROTO
Choose the VLAN protocol to use. At the time of writing, the kernel accepts only 802.1Q or 802.1ad.
priority VLANPRIO
Choose the VLAN priority to use. Decimal number in range of 0-7.
CONTROL
How to continue after executing this action.
reclassify
Restarts classification by jumping back to the first filter attached to this action's parent.
pipe Continue with the next action, this is the default.
drop Packet will be dropped without running further actions.
continue
Continue classification with next filter in line.
pass Return to calling qdisc for packet processing. This ends the classification process.
EXAMPLES
The following example encapsulates incoming ICMP packets on eth0 from 10.0.0.2 into VLAN ID 123:
#tc qdisc add dev eth0 handle ffff: ingress
#tc filter add dev eth0 parent ffff: pref 11 protocol ip
u32 match ip protocol 1 0xff flowid 1:1
u32 match ip src 10.0.0.2 flowid 1:1
action vlan push id 123
Here is an example of the pop function: Incoming VLAN packets on eth0 are decapsulated and the classification process then restarted for
the plain packet:
#tc qdisc add dev eth0 handle ffff: ingress
#tc filter add dev $ETH parent ffff: pref 1 protocol 802.1Q
u32 match u32 0 0 flowid 1:1
action vlan pop reclassify
SEE ALSO
tc(8)
iproute2 12 Jan 2015 VLAN manipulation action in tc(8)