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Configuration Guides

General Recommendations

IPv4 ARP & IPv6 Neighbor Timeout

Each equipment vendor implements its own maximum ages for the IPv4 ARP and IPv6 neighbor caches. The values vary widely and in at least one case (Linux) it is not a constant. Low ARP timeouts can lead to excessive ARP traffic, especially if the values are lower than the BGP keepalive intervals.

Conversely, long timeouts can theoretically lead to longer downtime if you change equipment. This is because your peers' routers still have the old MAC address in their ARP cache.

We recommend setting the ARP cache timeout to at least two hours, preferably four. See the sections on specific equipment vendors for examples.

Peering Network Prefix

The 48 IX Peering Network Prefixes is part of AS62484, and should not be globally routable. As such, the following guidelines should be followed when configuring your equipment:

  • Do not announce 48 IX networks in your router's BGP configuration.
  • Do not redistribute the route, a supernet, or a more specific prefix outside of your AS. We announce peering LAN prefixes with a no-export community — please honor it.


All 48 IX Exchange ports are configured with an MTU of 9216 bytes. It is recommended that member ports be configured with an MTU of 9000, leaving enough overhead for future protocols which may be used by the exchange.

Physical Connection

48 IX policy dictates that up to two MAC addresses are allowed behind a member port. This means that you'll need to be extremely careful when connecting a device that can act as a L2 device. Instabilities in a layer 2 network outside of our control can and typically do have a significant impact on the exchange as a whole. Bridging loops and spanning tree topology changes are good examples of this.

An intermediate L2 device may only bridge frames from the member's router(s) to the 48 IX port, and should otherwise be completely invisible. No connected device should bridge frames from other devices onto the 48 IX network, or send STP traffic on its 48 IX port.

Connecting a Layer 3 Device

The most preferred way to connect to 48 IX is to directly connect a layer 3 device (router) to your cross connect. This nearly automatically ensures:

  • Eliminates any risk associated with bridging two layer 2 domains
  • No STP traffic ingresses the port, removing any filtering overhead from the switch fabric
  • Easier troubleshooting in the event of connectivity or traffic flow issues
MemberRouter48-IXSwitchCross Connect

Connecting a Layer 2 Device

While we don't recommend connecting router router to 48 IX via an intermediate layer 2 device, keep the following mind should you choose to do so:

  • You must guarantee that only traffic to/from your router's IX interface goes to/from the 48 IX port
  • IGMP/MLD snooping on the intermediate switch may block legitimate ICMPv6 neighbor solicitations
  • You must disable spanning tree on your port facing 48 IX.

Spanning Tree

48 IX ports are configured with Spanning-Tree BPDU Guard/Protection, which means a port will be immediately shut down if STP frames are received on the port.

We strongly recommend using a dedicated VLAN for the path from your router to the 48 IX port.

MemberRouter48-IXSwitchCross ConnectMemberSwitch

Cisco Ios Configuration Examples

Cisco IOS devices tend to come with lots of features silently enabled which are generally unneeded, and may cause problems when connecting to an internet exchange. The following configurations may be more verbose than your typical configuration standards, but they will ensure no problematic traffic enters the IX.

Router Interface

interface Ethernet0/0
   mtu 9000
   no keepalive
   no cdp enable
   no mop enabled
   no lldp receive
   no lldp transmit
 ! IPv4
   no ip redirects
   no ip proxy-arp
   no ip directed-broadcast
   ip address
 ! IPv6
   ipv6 enable
   no ipv6 pim
   no ipv6 mld snooping
   ipv6 nd suppress-ra all
   ipv6 address 2001:db8:48:1::40/64

Switch Interface

vlan 3800
 name 48ix
vtp mode transparent
no spanning-tree vlan 3800
interface Ethernet0/0
  no keepalive
  no cdp enable
  no udld enable
  no lldp receive
  no lldp transmit
  switchport nonegotiate
  switchport mode access
  switchport access vlan 3800
  spanning-tree bpdufilter enable

Juniper Junos Configuration Examples

Global Configuration

set system arp aging-timer 240