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[QFX] How to determine the space utilized by a prefix in UFT in QFX5100

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Article ID: KB36544 KB Last Updated: 15 Jun 2021Version: 1.0
Summary:

This article details how to determine the space utilized by a prefix in the Unified Forwarding Table (UFT) in QFX5100 Series devices.

Solution:

The following table represents the memory utilized for programming a single prefix/route across route types and UFT profiles:

To determine the memory utilized for programming a single prefix, use the following procedure:

Note: For this example, the following hardware and Junos OS was used:

labroot@QFX51xx-R5> show version
Feb 19 19:23:03
fpc0:
--------------------------------------------------------------------------
Hostname: QFX51xx-R5
Model: qfx5100-48s-6q
Junos: 14.1X53-D35.3

Outputs with the default IPV4 host routes/before any IPV4 routes are advertised:

labroot@QFX51xx-R5> show pfe route summary hw ----> Displays routes installed in the on-chip hardware table

Slot 0
Unit: 0
Profile active: lpm-profile
Type            Max       Used      Free      % free
----------------------------------------------------
IPv4 Host       16384     14        16362     99.87   ----> Default free space
IPv4 LPM        131072    5         131067    100.00
IPv4 Mcast      8192      0         8181      99.87
-----snip-----

{master:0}
labroot@QFX51xx-R5> show pfe route summary ----> Displays summary of Packet Forwarding Engine information
Slot 0

IPv4 Route Tables:
Index         Routes     Size(b)
--------  ----------  ----------
Default           12        2352  ----> Default value
1                 11        2152
-----snip-----

Outputs when one IPV4 host route is advertised:

{master:0}
labroot@QFX51xx-R5> show pfe route summary hw ----> Displays routes installed in the on-chip hardware table
Slot 0
Unit: 0
Profile active: lpm-profile
Type            Max       Used      Free      % free
----------------------------------------------------
IPv4 Host       16384     15        16361     99.86  ----> Used value has increased by 1 and Free value has reduced by 1.
IPv4 LPM        131072    5         131067    100.00
IPv4 Mcast      8192      0         8181      99.87
-----snip-----

labroot@QFX51xx-R5> show pfe route summary ----> Displays a summary of Packet Forwarding Engine information.
Slot 0
IPv4 Route Tables:
Index         Routes     Size(b)
--------  ----------  ----------
Default           13        2548 ----> Routes value has increased by 1 and Size(b) has increased by 196.
1                 11        2152
-----snip-----

The same can be followed for other route types to determine their space utilization.

When the route threshold/space utilization exceeds the supported value, logs similar to the ones mentioned below are seen and hardware programming of new routes will fail:

Jan 17 08:50:49 2021  QFX51xx-R5 fpc0 _soc_alpm_128_insert: Unable to add newpivot to tcam
Jan 17 08:50:49 2021  QFX51xx-R5 fpc0 (brcm_rt_ip_uc_lpm_install:LPM route add failed) Reason : Table full
Jan 17 08:50:49 2021  QFX51xx-R5 fpc0 brcm_rt_ip_uc_entry_install Error: lpm ip route install failed vrf 1 ip 2007:0:500::/48 nh-swidx 131116 nh-hwidx 100045
Jan 17 08:50:49 2021  QFX51xx-R5 fpc0 _soc_alpm_128_insert: Unable to add newpivot to tcam


labroot@QFX51xx-R5> show pfe route summary hw ------> Displays routes installed in the on-chip hardware table
Slot 0
Unit: 0
Profile active: lpm-profile
Type            Max       Used      Free      % free
----------------------------------------------------
IPv4 Host       16384     3560      11276     68.82
IPv4 LPM        131072    1527      129545    98.83
IPv4 Mcast      8192      209       5638      68.82
 
IPv6 Host       8192      565       5638      68.82
IPv6 LPM(< 64)  16385     26801     0         0.00  --------> No free space
IPv6 LPM(> 64)  16385     172       0         0.00  --------> No free space
IPv6 Mcast      4096      0         2820      68.85

Route scale is higher for IPV6, which lead to a lack of space in the hardware table.

labroot@QFX51xx-R5> show route summary ------> Displays summary statistics about the entries in the routing table
----- snip ------
inet6.0: 106429 destinations, 106732 routes (106429 active, 0 holddown, 0 hidden)
Restart Complete
              Direct:     20 routes,     12 active
               Local:     18 routes,     18 active
                BGP: 106533 routes, 106238 active --------> BGP IPV6 routes are exceeding the threshold [default Limit - IPv6 unicast routes: 64,000 prefixes]
               IS-IS:    161 routes,    161 active
----- snip ------

Reduce the number of IPv6 routes learned either through route summarization or route aggregation to address the above issue.

UTF Profile Best Practice

If the host or LPM table stores the maximum number of entries for any given type of entry, the entire shared table will be full and will be unable to accommodate any entries of any other type. Different entry types occupy different amounts of memory. Visit Understanding the Unified Forwarding Table for more information.

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