joel jaeggli wrote:
> sure l3 acls can be applied to l2 ports.
> 
> most ixps are going to have a set of filters that prevent certain kinda
> of activity, e.g. spanning tree PDUs, router-advertisement, proxy-arp
> and so  on. these are all within the technical capabilties of most
> high-end-ethernet switch platforms.

this is a vast overstatement of ingress port filtering capabilities.
STP BPDUs are ignored because disabling STP on a port will cause the
packet to be silently dropped.  Most hardware which uses tcam for acls
will choke on even ostensibly simple configs, e.g. uniquely keyed L2 +
ipv4/ipv6 + L4 port filters applied on all ports.  Inspecting deep into
packets is rarely easy.  Overall the entire area is fraught with
limitations and corner cases.

Nick

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