![]() ![]() A Syslog message appears, informing us that the Loopback1 interface has come up. Jan 4 09:39:01.352: LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up. Users may assume that IPv4 and IPv6 address queries for localhost names will always resolve to the respective IP loopback address. No packet fragmentation or VPLS Control word bullshit nor frame drops nor MTU mismatch. Let’s create a loopback interface with an interface number of 1: R1 (config)interface loopback 1. I understand your confusion indeed for what I read from the rfc6761 about 'Special-Use Domain Names' 6.3, about the name localhost. Nothing breaks, because layer 3 MTU matches correctly between each termination 元, so PMTUD does it's job. My loopbacks are all 9k 元 MTU, most of my paths are 9k 元 MTU back-to-back, but some paths are 1500, some paths like wireless are 1500 on layer 3, but 1600 on layer 2 on the radios, but 9k L2 and 元 MTU on the transport ports on my PE router and P for example. When you add an address on the loopback interface with e.g. Don't justify to yourself with this "1600" cap, do 9k MTU on the PHYs everywhere when possible to ensure future overhead room for anything. When you ping 10.0.3.2, the reply does not come from some external device, but from the loopback interface itself. MTU itself is a piece of cake, however, when your network has all types of devices with varying MTUs, proper planning is required. fill out the form & at the Extended commands choose/type Y and enter the source address. MTU design and training, is often something I don't see very often in network training programmes and certs. Any traffic that a computer program sends on the loopback network is addressed to the same computer. Most IP implementations support a loopback interface (lo0) to represent the loopback facility. 元 MTU should be 9k in the backbone on the physical ports, but you cap it wherever required on the layer 3 sub interface, such as LACP bonding to your upstream devices or the 元 VLAN interface towards another device etc The Internet Protocol (IP) specifies a loopback network with the (IPv4) address 127.0.0.0/8. PMTUD works correctly in ALL paths and directions (MPLS TE? LDP? OSPF? BGP? GRE? WireGuard? Bridge, VLAN, VPLS? Etc)Ģ. Layer 3 MTU needs to be designed in a way that it ensures:ġ. I mean, wireless paths, technically, can do 9k MTU for layer 2 if the vendor supports, like some units from Ubiquiti.īut the point is, layer 2 MTU should always be MAXED out on ALL Devices, even if it's different between them. To summarize, this is basically the equivalent of wanting to write every number 1 to 100, but instead of writing out every number individually, instead you write 1, 2, 3.Yes, it matters. This two-colon replacement may only be applied once inĪn address, because multiple occurrences would create an ambiguous This is because ping on Windows Vista and newer Windows uses IPv6 by default when available.::1 is a shortened notation of IPv6 loopback address - equivalent of IPv4 loopback 127.0.0.1. The loopback address for IPv4 could take any value in the subnet 127.0.0.0/8 The loopback address for IPv6 could take any value in the subnet ::1/128 ping any value in those range should work if your network stack is working on your OS. Unspecified address, 0:0:0:0:0:0:0:0, are reduced to ::1 and ::, A loopback address is an address used by the system to validate the network stack of the OS. ![]() If you'd like screenshots, a guide from Microsoft can be found here: link.Īdditionally, you may also want to take a look at the Wikipedia Page for IPv6, specifically, Presentation:
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