[c-nsp] ASR920 - ingress/egress MPLS label limit

[James Bensley]

On 30 January 2017 at 08:45, Marcin Kurek <md.kurek at gmail.com> wrote:
> Hi all,
>
> I came across the following label allocation limit on ASR920
> (ASR-920-24SZ-IM) platform:
>
> ASR920#show platform hardware pp active sdm current
> CYLON_NUM_MPLS_INGRESS_LABELS        =      38912
> CYLON_NUM_MPLS_EGRESS_LABELS         =      28500
>
> I understand that egress labels are locally generated labels advertised to
> peers. Ingress labels are received from remote peers. What I don't
> understand is how to interpret this ingress limit.
>
> If there is a limit on labels received from peers, does it affect VPN labels
> too? For example, if I receive 10 000 prefixes from remote PE (per-prefix
> label allocation), does it mean that I've just used 10 000 out of 38912
> limit?

I would also like some clarity on this but yes I believe that is how
it works. If you are using per-prefix labelling and receive 10k
labelled routing advertisements that is 10k of your egress label space
gone.

The ME3600X/ME3800X actually have one shared MPLS space in TCAM. The
ME3600X for example is listed as having a 22,000 label limit by
default and the output from "show mpls label range" shows the usable
label range as 16 to 21999 (so just under 22k). If you look at the
TCAM with "show platform aspdma template | i MPLS" you can see they
can hold a total of 28.6k MPLS labels however only 22K of them can be
used for local labels (ingress labels) but up to 28.5k can be used for
egress labels.

ME3600X:
#sh platform aspdma template | i MPLS
…
NILE_NUM_MPLS_INGRESS_LABELS             =  22000
NILE_NUM_MPLS_EGRESS_LABELS              =  28500
…
EMPLS3LD_TABLE                                = 28672

So of the maximum 28.6k labels it can store no more than 22k of them
can be ingress labels and no more than 28.5k can be egress labels.

I have some more notes here if you’re board:
https://null.53bits.co.uk/index.php?page=inter-as-mpsl-optionb-mpls-label-usage

Since the ASR920 uses the Cylon ASIC which is like a “NILE version 2”
perhaps they also have the same behaviour?

The stats Cisco gave us were:
MPLS Ingress Labels 16,000
MPLS Egress Labels 28,000

ASR920#show mpls label range
Downstream Generic label region: Min/Max label: 16/32767

^ That says to me that 32k ingress / local labels can be assigned?

ASR920#show platform hardware pp active sdm current | i MPLS
CYLON_NUM_MPLS_INGRESS_LABELS        =      38912
CYLON_NUM_MPLS_EGRESS_LABELS         =      28500

^ This however says to me that 38.9k can be assigned?

It’s not clear how many labels have been assigned either:

"show platform hardware pp active tcam usage" isn't showing MPLS usage.

"show platform hardware pp active tcam utilization ?" isn't showing MPLS usage.

ASR920#show platform hardware pp active resource-usage summary 0 | i Type|MPLS
Type             Maximum     Allocated   Freed       In Use
Available for use
EMPLS3LD    ...  26624       100350      98663       1687        24937
EMPLSINTD   ...  8192        2660        2549        111         8081

EMPLS3LD, is that saying a max of 26k labels?

Perhaps one for Warris et al.

Cheers,
James.