[SANOG] MTU and MSS
ceo at teds.pk
Sat Aug 3 00:26:00 UTC 2013
May I add one more aspect, that is, SDH/DWDM transmission using Ethernet
encapsulation. Sometimes service degradation happens due to mismatch of MTU
size on Router interface and Tx interface and they always prefer jumbo
frames rather MTU 1500 bytes tradition.
On Saturday, August 3, 2013, Joe Abley wrote:
> Hi Simon,
> MTU is an IP-later interface parameter which indicates the largest
> datagram that can be transmitted without fragmentation. The minimum for
> IPv4 is 576 bytes; the minimum for IPv6 is 1280 bytes.
> 1500 is a common default value; it corresponds to the largest frame
> (without support for jumbograms, 802.1q or other link-layer encaps)
> accepted on 100M Ethernet.
> Many systems will allow the MTU to be adjusted between the IP-specified
> minimum and the maximum allowed by the link layer being used.
> MSS is a TCP parameter. It denotes the largest datagram size
> (pre-fragmentation) used to transmit a TCP segment.
> If you know that your path commonly includes a link with an MTU lower than
> that seen directly by clients, e.g. a 1480 byte MTU on a PPPoE link to the
> Internet from a gateway router, you can decide to lower the MSS on clients
> behind the gateway to avoid fragmentation at the gateway. Sometimes this is
> done on the gateway as a pragmatic (if layer-violating) measure.
> Fragmentation happens differently in v4 than it does in v6. Both have
> their problems. Fragmentation in general is known to cause performance
> problems in the real world, and there are often advantages in taking steps
> to avoid it.
> Aue Te Ariki! He toki ki roto taku mahuna!
> On 2013-08-02, at 16:43, "Simon Sohel Baroi / IIG-ITC / Sr.Manager /
> 'simon.baroi at fiberathome.net');>> wrote:
> Hi All,
> Can any one help me to understand about MTU and MSS.
> What should be the best value for MTU ?
> In my router interface I found its 1500, if I increase it or decrease it,
> does it put any effect to the CPU ?
> Does increasing MTU size help me for better browsing experience ? like
> I'm using these routers as an Internet Gateway.
> - with regards
> *Simon Sohel Baroi *| Sr. Manager, Technology | PICO | ITC - IIG |
> Cell : +880-1678-618243, +880-181-7022207 | Desk : +880-9666776677
> Ext-1031 |
> 'simon.baroi at fiberathome.net');> | Skype : tx.fttx |
> Reduce. Reuse. Recycle. Respect. It's the little things that really can
> make a difference.
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