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Showing posts from June, 2011

Private VLANs

Introduction To begin with, recall that VLAN is essentially a broadcast domain. Private VLANs (PVANs) allow splitting the domain into multiple isolated broadcast “subdomains”, introducing sub-VLANs inside a VLAN. As we know, Ethernet VLANs can not communicate directly with each other – they require a L3 device to forward packets between separate broadcast domains. The same restriction applies to PVLANS – since the subdomains are isolated at Level 2, they need to communicate using an upper level (L3/packet forwarding) device – such as router. In reality, different VLANs normally map to different IP subnets. When we split a VLAN using PVLANs, hosts in different PVLANs still belong to the same IP subnet, yet now they need to use a router (L3 device) to talk to each other (for example, by using Local Proxy ARP). In turn, the router may either permit or forbid communications between sub-VLANs using access-lists. Commonly, these configurations arise in “shared” environments, say ISP co-locat...
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MLPPP LFI

Looks like this is one of the tricky small topics which every ccie r&s candidate should know. So imagine the following scenario. You have two routers R4 and R5 with serial interface and you have to configure multilink interleaving and fragmentation. One of the most important thing you should remember is that the interleaving is working only on "fair-queue" enabled interfaces. So usually the tricky question is when you are asked to configure frame relay traffic shaping and enable the ppp multilink interleaving and fragmentation(which will be automatically configured for you if you don't specify it) so, the first thing that you have to remember is if you have frame relay traffic-shaping it will disable the fair queue on the interface. So what we should do is to configure the interleaving on the Multilink interface. So there is the configuration output example: [I am using Internetwork Expert R&S Workbook 1, task 10.55, version of the document 5.019] Also in this par...
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basic MPLS VPN scenario

It's really basic topology with two VPN clients. I decided to use VRF CLIENT_A and VRF CLIENT_B; CLIENT_A is running OSPF and CLIENT_B is running BGP. There is another link between SW3 and SW2. I have configured sham-link to avoid it. Something interesting and maybe a common mistake is when you configure the sham-links to use wrong "area id" and what would happen is that the routes in your fib table will appear as INTER-AREA routes instead of INTRA-AREA routes. There is nothing specific about VRF CLIENT_B, anyway, if someone is digging and looking for some scenario maybe this picture will be useful.
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