setting fragmentation on MLPPP

[fprime7]

Hi

I need to set the fragmentation for a Multilink interface for 350 Bytes that has 4 T1s

Is that done on the Serial T1 interface or the PPP Multilink Interface ?

what would be the commands, currently PPP Multilink shows fragmentation

1496 frag size

Thanks

Frank

[pkhatri · Accepted solution]

Hi Frank,

You need to configure the fragment size using the ppp multilink fragment delay command under the PPP multilink interface.

Paresh.

PS. Pls do remember to rate posts

[fprime7]

Hi Paresh

How would I calculate the delay to handle only 350 bytes on a Multilink bundle with just one T1 in the bundle

I see the example on the Cisco web site

ppp multilink fragment delay 20

not sure how to figure out the delay

Thanks

Frank

[smothuku · Accepted solution]

Hi Frank ,

ppp multilink fragment size :

To specify the maximum packet fragment size in bytes for a Multilink PPP (MLP) link, use the ppp multilink fragment size command in interface configuration mode.

Use the ppp multilink fragment size command to specify a maximum fragment size that is smaller than the size automatically computed by the value set with the ppp multilink fragment delay command. The ppp multilink fragment size command may be configured on the bundle interface or on the member links. If the command is configured on the bundle interface, the same fragment size is used by all of the links in the bundle. If it is configured in both places, the configuration on the member link takes precedence.

Examples

The following example configures a maximum fragment size of 100 bytes, not including link layer or multilink header overhead:

ppp multilink fragment size 100

ppp multilink fragment delay :

To specify a maximum time for the transmission of a packet fragment on a Multilink PPP (MLP) bundle, use the ppp multilink fragment delay command in interface configuration mode.

The default value is 30 milliseconds if interleaving is enabled or if the bundle contains links that have differing bandwidths. See the "Usage Guidelines" for more information.

check the below link

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tdia_r/dia_p2ht.htm#wp1042547

and

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/dial_r/drprt2/drppp.htm#wp5253

Hope it helps you.plz rate it.

Thanks,

satish

[fprime7]

Hi Satish,

I am running IOS 12.3(11)T2 on Cisco 7204VXR

and do not have the command

ppp multilink fragment size ##

on either the Multilink or Serial interfaces

only can set the

ppp multilink fragment

delay

disable

maxium - specify # of fragments per transmitted packets

Any other commands to set fragment size

Thanks

Frank

[smothuku]

Hi Frank,

I think ppp multilink fragment size is not supported in 7204vxr router.You can see either ppp multilink fragment disable or no ppp multilink fragment command under multilink config.

You can configure ppp multilink fragment

delay under multilink interface.

I will check alternate command for "ppp multilink fragment size " in 7204VXR

Thanks,

satish

[pkhatri · Accepted solution]

Hi Frank,

You can still use the ppp multilink fragment delay command. In order to get a fragment size of 350 bytes, you will need to set a delay which results in that fragment size. For a T1 link:

1536000/8 = 192000 bytes

Therefore, to get a fragment size of 350 bytes, the delay has to be 350/192000, which gives you 1.82ms. Since the granularity of the delay is in milliseconds, the best you can do is set it to 2ms, which will give you an actual fragment size of 384 bytes.

Hope that helps,

Paresh

[fprime7]

Thanks

after I set the fragment delay to 2 ms

the multilink showed

384 weight, 376 frag size

what is the weight ?

[smothuku · Accepted solution]

Hi Frank ,

Fragment weight = ((fragment-delay) x (link speed) / 8).

In your case , weight = ((2x1544)/8) =386.

Example for better understanding :

If 'ppp multilink fragment-delay' is not explicitly set,it uses the default value of 30 ms. With this value of fragment delay and T1 interface speed (my routers were defaulting to 1544K bandwidth speed (even though useable is only 1536K (1544K - 8K framing)), this would result in a fragmentation weight size of 5790(30x1544 /8) and a fragment size (upper limit at which fragmentation will occur) of 1496 bytes. Packets approaching this 1496 and above (1500), will be fragmented. Weight again

being determined by physical interface bandwidth and fragment-delay value. With enabling 'interleaving', having MLP member interfaces with differing bandwidths, or explicitly setting the 'ppp multilink fragment-delay' results in this load distribution algorithm method of using a weight for each physical link member of the bundle.

weight ((fragment-delay) x (link speed) / 8)

Hope it clarifies you.

Thanks,

satish