[j-nsp] J6350 Jumbo frame MTU and OSPF setting

Sat Oct 2 00:35:27 EDT 2010

Hi Ben,

Thanks for your hits. I can configure the fiber PIMs to MTU 9018 and able
to ping other J6350 with ICMP packet over 8000 bytes with do-not-fragment.

Physical interface: ge-3/0/0, Enabled, Physical link is Up
  Interface index: 152, SNMP ifIndex: 184
  Description:
  Link-level type: Ethernet, MTU: 9018, Speed: 1000mbps, BPDU Error: None,
MAC-REWRITE Error: None,
  Loopback: Disabled, Source filtering: Disabled, Flow control: Enabled,
Auto-negotiation: Disabled,
  Remote fault: Online
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Current address: b0:c6:9a:87:35:36, Hardware address: b0:c6:9a:87:35:36
  Last flapped   : 2010-09-27 02:32:24 UTC (5d 01:50 ago)
  Input rate     : 0 bps (0 pps)
  Output rate    : 1672 bps (3 pps)
  Active alarms  : None
  Active defects : None

ping XXX.XXX.XXX.254 size 8976 do-not-fragment
PING XXX.XXX.XXX.254 (XXX.XXX.XXX.254): 8976 data bytes
8984 bytes from XXX.XXX.XXX.254: icmp_seq=0 ttl=64 time=77.341 ms
8984 bytes from XXX.XXX.XXX.254: icmp_seq=1 ttl=64 time=77.758 ms
8984 bytes from XXX.XXX.XXX.254: icmp_seq=2 ttl=64 time=77.487 ms
^C
--- XXX.XXX.XXX.254 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 77.341/77.529/77.758/0.173 ms

However, increasing the MTU size on both the J6350s may not be able to get
a better TCP throughput, because the Host NICs and Switchport are also
using MTU 1500 right? Should I change the MTU size on Host NICs and Juniper
EX switches to MTU 9018 in order to prevent the frame fragmentation
happened below 9018?

Please advise.

Thanks
- Harris

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  |Ben Dale <bdale at comlinx.com.au>                                                                                                                   |
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  |Harris Hui/Hong Kong/IBM at IBMHK                                                                                                                    |
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  |juniper-nsp at puck.nether.net                                                                                                                       |
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  |10/01/2010 PM 07:46                                                                                                                               |
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  |Re: [j-nsp] J6350 Jumbo frame MTU and OSPF setting                                                                                                |
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Hi Harris

My apologies, I completely missed the fact that you were using fiber PIMs -
maximum MTU for these is 9018 or 9014 if you have the multi-port version:

http://www.juniper.net/techpubs/software/junos-security/junos-security10.0/junos-security-swconfig-interfaces-and-routing/interfaces-physical-properties-section.html#interfaces-mtu-section

On 01/10/2010, at 8:36 PM, Harris Hui wrote:

      Hi Ben,

      Looks like I can apply the MTU setting on the reth interface but
      cannot apply it on the fiber modules.

      show interfaces reth4
      Physical interface: reth4, Enabled, Physical link is Up
      Interface index: 132, SNMP ifIndex: 180
      Link-level type: Ethernet, MTU: 9192, Speed: 1000mbps, BPDU Error:
      None, MAC-REWRITE Error: None, Loopback: Disabled,
      Source filtering: Disabled, Flow control: Disabled, Minimum links
      needed: 1, Minimum bandwidth needed: 0
      Device flags : Present Running
      Interface flags: SNMP-Traps Internal: 0x4000
      Current address: 00:10:db:ff:70:04, Hardware address:
      00:10:db:ff:70:04
      Last flapped : 2010-10-01 10:24:25 UTC (00:03:48 ago)
      Input rate : 264 bps (0 pps)
      Output rate : 480 bps (0 pps)

      Thanks
      Harris

      <graycol.gif>Ben Dale ---10/01/2010 PM 02:11:40---Hi Harris

 <ecblank.gif>     <ecblank.gif>                                           
 From:             Ben Dale <bdale at comlinx.com.au>                         

 <ecblank.gif>     <ecblank.gif>                                           
 To:               Harris Hui/Hong Kong/IBM at IBMHK                          

 <ecblank.gif>     <ecblank.gif>                                           
 Cc:               juniper-nsp at puck.nether.net                             

 <ecblank.gif>     <ecblank.gif>                                           
 Date:             10/01/2010 PM 02:11                                     

 <ecblank.gif>     <ecblank.gif>                                           
 Subject:          Re: [j-nsp] J6350 Jumbo frame MTU and OSPF setting      

      Hi Harris

      On 01/10/2010, at 3:35 PM, Harris Hui wrote:

      > I am trying to configure our J6350 fiber interface to MTU 9192 to
      get a
      > better TCP throughput. However, I can only able to configure the
      MTU size
      > below 1500, when I configure the MTU to 9192 and commit the
      changes, it
      > still shows MTU 1500 on the physical interface.

      I've only got a 2320 in front of me right now, but your configuration
      below works fine (and the MTU changes) - what version of JUNOS are
      you running?

      > Do you have any experience on using Jumbo frame MTU size on the
      J6350? We
      > are also running OSPF across the private circuit, is JUNOS support
      "OSPF
      > ignore-mtu" like cisco?

      No and we've been bitten by this before - I have raised an ER with my
      SE regarding this, but who knows how far away that will be.  You
      shouldn't need to use it if you control the routers on both ends (and
      the issue you are having with MTU goes away).

      Cheers,

      Ben

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