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eesun_276598's avatar
eesun_276598
Icon for Cirrus rankCirrus
Dec 06, 2017

VLAN ID and tag

Hi Anyone can make it clear the concept with relation between VLAN ID and its tag in f5. In Cisco switch, vlan id is vlan number, such as vlan 10, vlan 20, vlan 30 etc. And tag is used when two switc...
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BIG-IP
Hannes_Rapp_162's avatar
Hannes_Rapp_162
Icon for Nacreous rankNacreous
Dec 15, 2017

I see others already did a pretty good job at explaining this (upvotes given as credit). I'll just summarize bits and pieces into one answer and elaborate.

As you seem familiar with Catalyst NS, I'll use this as point of reference. In Catalyst switches, your default VLAN is VLAN 1 which is also the default 

Native VLAN
. In a dot1q Ethernet link, just one VLAN can be untagged, otherwise the switch that receives a frame wouldn't be able to tell to which VLAN the received frame belongs to. So in case of Cisco Catalyst switches, all VLAN 1 traffic is untagged by default for any dot1q links you create. It's also a common security practice to change native VLAN to something other than VLAN 1.

In a Catalyst NS, you can change your native (aka untagged) VLAN with 

switchport trunk native vlan
command (if-config). So if you type in 
switchport trunk native vlan 10
, your VLAN10 traffic on that dot1q link would become untagged, and VLAN 1 traffic would become tagged as a result. In case of BigIP LTM, moving VLAN 10 to untagged is the exact same thing. 
Untagged VLAN
is 
Native VLAN
.

As you are familiarizing yourself with BigIP L2 terminology, keep in mind that F5 has a tendency to vandalize commonly accepted networking terminology. I.e., "Trunk" term here means something completely different. It is used to describe 

Link Aggregation
(known as EtherChannel in Cisco world).

  • Stanislas_Piro2's avatar
    Stanislas_Piro2
    Icon for Cumulonimbus rankCumulonimbus
    Dec 15, 2017

    As you are familiarizing yourself with BigIP L2 terminology, keep in mind that F5 has a tendency to vandalize commonly accepted networking terminology.

     

    I should replace commonly accepted with Cisco

     

    When searching over Internet the definition of Trunk in networking terminology, I found several articles with this kind of explanation (this one is from wikipedia):

     

    In computer networking, port trunking is the use of multiple concurrent network connections to aggregate the link speed of each participating port and cable, also called link aggregation. Such high-bandwidth link groups may be used to interconnect switches or to connect high-performance servers to a network.

     

    Cisco made some weird choices all other vendors can disallow...

     

    How many times I heard some network engineers talking about Source NAT and calling it PAT!!!

     

    Why Cisco named source NAT with the name of the workaround?

     

  • Hannes_Rapp_162's avatar
    Hannes_Rapp_162
    Icon for Nacreous rankNacreous
    Dec 15, 2017

    Hahah

     

    The way I see it, F5 would ideally use "Port Aggregation" or "Link Aggregation" for absolute clarity. Or by minimum, "Port Trunk" over "Trunk". "Trunk" word alone is vandalized so much in networking that it's stripped of any meaning. Another word must at all times stand next to it. Cisco is so big that if they are first to vandalize a term, the vandalized variant almost always becomes the new norm. Possibly thats why when talking about "Trunk", the first thing that comes to a network guy's mind is the Cisco's VTP protocol and VLAN trunking. As you pointed out, "Port trunking" is also a real deal. Not a completely made up thing, but also no longer the winning candidate for it's shorter abbreviation "trunk".

     

    If we add another vendor to mix, CheckPoint, things get really exciting! They use term "bond" which stands for an aggregated link and "bonding" which stands for link aggregation. Complete mess! Maybe the network tech guys will one day come to senses and stop inventing new terms for link aggregation. As the saying goes, a good kid has many names but this is being taken too far!