Re: [load balancing] BigIP's and trunking

From: Tim Maestas (
Date: Wed Jan 16 2002 - 23:03:31 EST

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    Thank you for the information. I am now much less confused. It seems
    what I'm looking for is not 802.1q VLAN tagging, so much as
    802.1ad/802.3ad link aggregations as in most of my BigIP configurations I
    only have 1 VLAN per interface.

    I understand what you're talking about regarding sessions using the same
    link in the trunk. From what I've read of Cisco's implementation of
    802.3ad (Fast/Gigabit Etherchannel) the switch determines what port in the
    trunk to switch the packet to by performing an XOR of the source and
    destination MAC addresses.

    A question: If I'm becoming concerned about bandwidth in and out of my
    BigIP's, would you think I'd be better off trunking 4 100Meg ports, or
    replacing my front and/or back interfaces with gig interfaces? Last I
    saw, I believe the gig cards sold by F5 can do somethingl like 340Megs
    tops, so from a strictly mathematical standpoint I'd get a bit more out of
    a 400meg trunk, but I'm wondering if there are any other factors I should
    be thinking about.

    Thanks again.


    On Wed, 16 Jan 2002, John Hall wrote:

    > Trunking is unfortunately an over-used word, causing much confusion
    > in the world today... :(
    > Your reference to 802.1q leads me to believe you are talking about the
    > trunks that are defined 802.1q Annex D where you have multiple tagged
    > VLAN's configured on a single interface in order to pass traffic for
    > multiple VLAN's between two switches. All BIG-IP versions after v3.1
    > support tagged VLAN's (although I have to admit the support got *MUCH*
    > better after v4.x) and assigning multiple VLAN's to a single interface
    > for the purpose of VLAN trunking (that's what *I* call this use).
    > Although I'm confused by your reference to "bandwidth aggregation".
    > Rick has already replied to you referring to our "bigpipe trunk"
    > command, which is used to configure 802.1ad Link Aggregations, which
    > are used to make multiple links (physical ports) operate as a single
    > interface providing the sum of the bandwidths of the aggregated links
    > to the interface and also providing link failure protection (if one
    > of several aggregated links goes down, the others continue to operate).
    > One practical note is that, like most 802.1ad implementations, ours
    > works most efficiently if the number of interfaces configured is a
    > multiple of two. Another quirk of 802.1ad that is often not known
    > is that all packets associated with a single IP connection (say a
    > single telnet session) are *always* sent on the same link of an
    > aggregation (this is required by the spec). So, if you setup a
    > link aggregation, using 4 100BaseTX ports, and try to download a
    > single huge file via FTP, that single download will only be allowed
    > approximately 100Mb/s of bandwidth, but if you have a bunch of sessions
    > going simultaneously, you will see all four links utilized.
    > Before you ask, yes, you can configure a single set of links (say four
    > 100BaseTX ports) to operate as an 802.1ad link aggregation (giving you
    > close to 400Mb/s of bandwidth on the interface) with multiple tagged
    > VLAN's going across that interface to another switch. One of our test
    > configurations uses four gigabit interfaces aggregated to a single
    > interface over which we pass traffic from four (two internal and two
    > external) VLAN's and it works like a charm. Link aggregation allows
    > you to use the full bandwidth capacity of your BIG-IP in a balanced
    > way when your traffic load is asymmetric (such as with web traffic
    > where the incoming requests are small, but the responses are large).
    > Hope this helps,
    > JMH
    > Tim Maestas wrote:
    > >
    > > I was wondering if anyone has had any experiences (good, bad, or
    > > otherwise) with using trunking under BigIP 4.x, in particular into a Cisco
    > > 6500 series switch. In reading the 4.x documentation, there is no mention
    > > of 802.1q trunk modes like there was in 3.x, so I'm not sure how I would
    > > be able to make my Cisco treat my trunked interfaces as a group. In 4.x
    > > it seems like outgoing packets from the BigIP would be
    > > "load-balanced" between the interfaces, but I don't see how this is
    > > possible for incoming packets, without something like 802.1q. Granted,
    > > if nothing else trunks will give me interface failover, but I'm looking
    > > more for bandwidth aggregation. Any info would be appreciated.
    > >
    > > -Tim
    > >
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