Re: LAN<-->WAN<-->LAN ; L3 switches or Routers??

Discussion in 'Cisco' started by thrill5, Jul 20, 2006.

  1. thrill5

    thrill5 Guest

    This is not entirely true. A "L3 switch" does not do QoS. Yes a "L3 Switch"
    can do QoS marking, but it cannot do policing, queuing (at layer 3) WRED,
    etc. A L3 switch does CoS (class of service), which is limited by hardware
    (number or receive queues, output queues and priority queues) on each port.
    FLEXWAN and OSM cards for the 6500 series are boards that let you do the
    same QoS stuff that you can do on router interface. Its also why they are
    big bucks.

    Scott
    "stephen" <> wrote in message
    news:cZctg.1221$...
    > "Merv" <> wrote in message
    > news:...
    >>
    >> > So something to consider is what hardware you need to interface to the

    > WAN.
    >>
    >> This is a good point as while Cisco high-end switches like the 6500
    >> have FLEXWAN card to support more than just Ethernet connectivity this
    >> is not the case on their low end switches.

    >
    > this is a good point to mention to the OP that the difference between
    > routers and L3 switches these days is more about marketing and the "bias"
    > in
    > the box design than engineering.
    >
    > originally - routers were basically software, and switches were hardware.
    > now boxes with reasonable performance are usually a "blend" somewhere
    > between those 2 extremes.
    >
    > the rule of thumb is that if all the interfaces are "lan like" - then it
    > probably gets called a switch, and if you are using older style WAN
    > interfaces such as T1 / E1, Frame Relay or ATM it probably is called a
    > router - but as other have said there are exceptions to both of these.
    >>
    >> So you might need routers and switches depending on the WAN transport
    >> options available.
    >>

    > --
    > Regards
    >
    > - replace xyz with ntl
    >
    >
    thrill5, Jul 20, 2006
    #1
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  2. thrill5

    stephen Guest

    "thrill5" <> wrote in message
    news:...
    > This is not entirely true. A "L3 switch" does not do QoS.


    as with most computer things "it depends" - it doesnt have to, but any high
    end network equipment these days that doesnt "do" QoS doesnt get bought -
    QoS features are mandatory when a company generates a tick list for a big
    procurement, and the manufacturers want their kit to get bought.

    Yes a "L3 Switch"
    > can do QoS marking, but it cannot do policing, queuing (at layer 3) WRED,
    > etc. A L3 switch does CoS (class of service), which is limited by

    hardware
    > (number or receive queues, output queues and priority queues) on each

    port.

    FWIW i just did a lot of lab testing on a Cat6, Sup 720-3B, 6724-SFPs.

    policing, Q managment (2 Qs inbound, 4 out), and WRR (which is sort of
    modified WRED) are all there.

    it is the same rich set of features as you get on a software router, but it
    did everything we wanted, apart from shaping to fractional Gig E while also
    doing QoS queue management.

    > FLEXWAN and OSM cards for the 6500 series are boards that let you do the
    > same QoS stuff that you can do on router interface. Its also why they

    are
    > big bucks.


    Agreed.

    in our case it was cheaper to use more bandwidth and do GigE "wire speed"
    across a WAN than to have the richer features needed to handle lower speed
    links.

    >
    > Scott
    > "stephen" <> wrote in message
    > news:cZctg.1221$...
    > > "Merv" <> wrote in message
    > > news:...
    > >>
    > >> > So something to consider is what hardware you need to interface to

    the
    > > WAN.
    > >>
    > >> This is a good point as while Cisco high-end switches like the 6500
    > >> have FLEXWAN card to support more than just Ethernet connectivity this
    > >> is not the case on their low end switches.

    > >
    > > this is a good point to mention to the OP that the difference between
    > > routers and L3 switches these days is more about marketing and the

    "bias"
    > > in
    > > the box design than engineering.
    > >
    > > originally - routers were basically software, and switches were

    hardware.
    > > now boxes with reasonable performance are usually a "blend" somewhere
    > > between those 2 extremes.
    > >
    > > the rule of thumb is that if all the interfaces are "lan like" - then it
    > > probably gets called a switch, and if you are using older style WAN
    > > interfaces such as T1 / E1, Frame Relay or ATM it probably is called a
    > > router - but as other have said there are exceptions to both of these.
    > >>
    > >> So you might need routers and switches depending on the WAN transport
    > >> options available.
    > >>

    > > --
    > > Regards
    > >
    > > - replace xyz with ntl
    > >

    --
    Regards

    - replace xyz with ntl
    stephen, Jul 21, 2006
    #2
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  3. thrill5

    J Guest

    stephen wrote:
    > FWIW i just did a lot of lab testing on a Cat6, Sup 720-3B, 6724-SFPs.
    >
    > policing, Q managment (2 Qs inbound, 4 out), and WRR (which is sort of
    > modified WRED) are all there.
    >
    > it is the same rich set of features as you get on a software router, but it
    > did everything we wanted, apart from shaping to fractional Gig E while also
    > doing QoS queue management.


    Comparing a 6500 to a just a router or just a switch is not a fair
    comparison. A 6500 contains both a router and a switch (plurality in
    some cases). There is no apples to apples comparison in a chassis that
    has MLS capabilities. If you want to compare a basic router and a
    basic switch then compare a 3825 without any EtherSwitch modules and a
    3750-EMI. That's a fair comparison between a router and a L3-switch.

    > > FLEXWAN and OSM cards for the 6500 series are boards that let you do the
    > > same QoS stuff that you can do on router interface. Its also why they

    > are
    > > big bucks.

    >
    > Agreed.
    >
    > in our case it was cheaper to use more bandwidth and do GigE "wire speed"
    > across a WAN than to have the richer features needed to handle lower speed
    > links.


    This makes good sense. I'm also opposed to blending network layers in
    large chassis. You could run an entire ISP out of a single 7600 but
    that would involve blending core, distribution, access, and border
    router functions (I always separate border routers into a 4th network
    layer) into a single chassis. That breaks most of the design
    principals of modern day LAN/WAN design. Just because the device
    you're working with can do routing, it doesn't make it a good router.
    Likewise for interfaces; just because you can put 16 FastEthernet
    interfaces in a router doesn't mean it makes a good switch. This also
    applies to circuits and their purposes. Just because you can get an
    Ethernet hand-off for your Internet circuit doesn't mean you should
    forego a real router and plug it into a L3 switch.

    One place that a WAN Ethernet hand-off does allow you to fudge on is
    firewalls. I don't have any problem at all with eliminating the border
    router for a small non-multi-homed office and replacing it with a
    purely-Ethernet firewall. There are design applications that may
    require a connection outside of the firewall but most of our customers
    don't have these requirements. If the hand-off had been a couple T1s
    they would have been stuck with a border router.



    J
    J, Jul 21, 2006
    #3
  4. thrill5

    stephen Guest

    "J" <> wrote in message
    news:...
    > stephen wrote:
    > > FWIW i just did a lot of lab testing on a Cat6, Sup 720-3B, 6724-SFPs.
    > >
    > > policing, Q managment (2 Qs inbound, 4 out), and WRR (which is sort of
    > > modified WRED) are all there.
    > >
    > > it is the same rich set of features as you get on a software router, but

    it
    > > did everything we wanted, apart from shaping to fractional Gig E while

    also
    > > doing QoS queue management.

    >
    > Comparing a 6500 to a just a router or just a switch is not a fair
    > comparison. A 6500 contains both a router and a switch (plurality in
    > some cases). There is no apples to apples comparison in a chassis that
    > has MLS capabilities. If you want to compare a basic router and a
    > basic switch then compare a 3825 without any EtherSwitch modules and a
    > 3750-EMI. That's a fair comparison between a router and a L3-switch.


    you are tlkaing about hybrid mode where you use CatOS for the L2 aspects of
    the switch and IOS on the MSFC to provide an embedded router. but you dont
    have to run a Cat6k like that - and in some configs you cant.

    when you use the DFC blade you run the Cat6k as an IOS only switch - it
    basically follows the same design as a 3750, just extra scale and some more
    flexibility.
    >
    > > > FLEXWAN and OSM cards for the 6500 series are boards that let you do

    the
    > > > same QoS stuff that you can do on router interface. Its also why

    they
    > > are
    > > > big bucks.

    > >
    > > Agreed.
    > >
    > > in our case it was cheaper to use more bandwidth and do GigE "wire

    speed"
    > > across a WAN than to have the richer features needed to handle lower

    speed
    > > links.

    >
    > This makes good sense. I'm also opposed to blending network layers in
    > large chassis. You could run an entire ISP out of a single 7600 but
    > that would involve blending core, distribution, access, and border
    > router functions (I always separate border routers into a 4th network
    > layer) into a single chassis.


    FWIW a 7600 is Cat6k, AFAIR just different chassis, vertical mounted blades
    and restricted to IOS only mode.

    That breaks most of the design
    > principals of modern day LAN/WAN design. Just because the device
    > you're working with can do routing, it doesn't make it a good router.
    > Likewise for interfaces; just because you can put 16 FastEthernet
    > interfaces in a router doesn't mean it makes a good switch. This also
    > applies to circuits and their purposes. Just because you can get an
    > Ethernet hand-off for your Internet circuit doesn't mean you should
    > forego a real router and plug it into a L3 switch.


    Actually we are delivering Internet access to customers at work - and often
    that is exactly what they do.

    For 10 and 100 M, it doesnt matter that much whether you have a router or a
    switch, since a mid range router like a 3845 is fast enough.

    A "real" router with the horsepower to terminate a GigE WAN link is an
    expensive toy - A stackable Cat has good enough forwarding to substitute
    (although there isnt as much software processing available, memory for
    routing tables etc) at a small fraction of the cost.

    >
    > One place that a WAN Ethernet hand-off does allow you to fudge on is
    > firewalls. I don't have any problem at all with eliminating the border
    > router for a small non-multi-homed office and replacing it with a
    > purely-Ethernet firewall. There are design applications that may
    > require a connection outside of the firewall but most of our customers
    > don't have these requirements. If the hand-off had been a couple T1s
    > they would have been stuck with a border router.
    >
    >
    >
    > J

    --
    Regards

    - replace xyz with ntl
    stephen, Jul 22, 2006
    #4
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