Hello guys, I would like to understand or find out where I can read about it regarding the router behaviour and how it treats incoming packets and does ARP resolution in these scenarios: R1--intF0/0---------------------------F0/0.10--R2, the interfaces are on the same network but it does not work, what R2 does when there is an incoming ARP request from R1 and how packets are treated and tied to a specific interfaces? R1--Global routing table---------------------------------------vrf--R2 And in this case how the ARP resolution is done, I found the articles explaining how it should be done, but for purposes of troubleshooting I would like to understand why the "how it should not be done" does not work, how to troubleshoot it and fix? What should I read to understand this? Thank a lot!! ... View more

Hello, Does anyone know if it is possible to redirect packets destined for a local loopback interface? My situation is the following: 1. I have an incoming IP packet destined to my loopback 2. Once it is decapsulated, inside there is an X25 packet which is routed via a local directly attached device (in fact the static route tells the route to forward the x25 packet to the directly attached serial device,otherwise the router does not know it) 3. I need to redirect this IP packet to another router and let it process the request and send the response to the destination directly or through my router, either way works well.. The main problem is to be able to redirect the packet. PBR does not work, it simply bypasses the PBR since it is destined to local loopback address... I searched through the internet and people say it does not work with PBR. Is there another way to do it? I am using  IOS 15.2(4)M1 in a virtualized environment, the production router I believe is running 15.x and it is a 37xx Thanks a lot!!! ... View more

Hello guys, I am trying to understand how ARP resolution works at an intermediate router which builds xconnect point-to-point session between a router that sends untagged traffic on one side and another one sending tagged traffic on the other.. Both edge routers cannot resolve ARP to ping each other.. The config I took from the cisco website from this article http://www.cisco.com/c/en/us/support/docs/routers/asr-9000-series-aggregation-services-routers/116453-technote-ios-xr-l2vpn-00.html 3.1.2 Subinterfaces and VLAN Manipulation I have the following topology attached The config is: R1---gi0/0/0/0-----------untagged---------------gi0/0/0/0---R2---git0/0/0/1-------------tagged------------------gi0/0/0/0---R3 It should work like this: 1) R1 sends untagged frame to R2 2) R2 should check the tcam to find the corresponding subinterface or interface to match the frame 3) When R2 finds that this subint corresponds to xconnect session: l2vpn  xconnect group test   p2p p2pGrupo    interface GigabitEthernet0/0/0/0.1    interface GigabitEthernet0/0/0/1.2 4) R2 should then tag the frame with ID of 2 and send it to R3 encapsulation dot1q 2  rewrite ingress tag pop 1 symmetric 5) When the answer is coming back from R3, it is coming tagged, the R2 based on "rewrite ingress tag pop 1 symmetric" shoul pop the tag and send it untagged to R1... But this does not happen.. 6) When pinging from R1 to R3 o viceverca, both of these routers never get an ARP reply and therefore cannot build a L2 frame 7) Before I had the xconnect session in Down state (because I did the lab the same way it was on Cisco website, but I think there is an error there. I built an xconnect session on R2 between R2´s Gi0/0/0/0 interface and G0/0/0/1.2 subint.. It did not establish the xconnect session.. Dont know why. After I configured xconnect between 2 subinterfaces, the xconnect session worked, but the frames still don´t go through.. Any advice on this issue? R1 interface GigabitEthernet0/0/0/0  cdp  ipv4 address 10.1.1.1 255.255.255.0 R2 interface GigabitEthernet0/0/0/0 ! interface GigabitEthernet0/0/0/0.1 l2transport ! interface GigabitEthernet0/0/0/1 ! interface GigabitEthernet0/0/0/1.2 l2transport  encapsulation dot1q 2  rewrite ingress tag pop 1 symmetric ! l2vpn  xconnect group test   p2p p2pGrupo    interface GigabitEthernet0/0/0/0.1    interface GigabitEthernet0/0/0/1.2 R3 interface GigabitEthernet0/0/0/1 ! interface GigabitEthernet0/0/0/1.2  ipv4 address 10.1.1.2 255.255.255.0  encapsulation dot1q 2 ... View more

Hello guys, I came across this issue, which I am not able to reproduce in the lab environment for now (since I do not know how to simulate an x.25 device to make a call to another end)... 1. There is an X.25 cashier (device) trying to communicate with the X.25 server through the IP/MPLS network. (which requires X.25 over TCP (xot) to be implemented) to make possible the X.25 traffic to travel through the IP cloud 2. The CPE cutomer router only receives R1 and R2 loopbacks 3. Impossibility to make config changes on the CPE router (which in fact are many routers installed in different places, all of them pointing to R1 and R2 loopbacks. ). 4. The PE R1 and R2 routers will be replaced by the new CE1 and CE2 routers, which are already installed and have all the routes 5. The idea is to do the following: a) Let the R1 or/and R2 still receive x.25 traffic through incoming XOT sessions b) Build another XOT session and redirect XOT traffic to new CE1 and/or CE2 routers c) Let the CE1 and/or CE2 routers to communicate with the X.25 servers and build another XOT session if necessary (for example to the CPE2 router, which finally communicates through x.25 with a directly connected x.25 server) d) when the R1 and R2 are removed, their Loopbacks will be moved to new CE1 and CE2 which should not affect the topology, since all the CPE routers point to these old loopbacks The question is: Is it possible from the technical point of view, build many XOT sessions, will it work? Any help is very appreciated!!! Thanks a lot! ... View more

Hello guys, I could never completely understand this point. This seems a bit contradictory for me. 1. On one hand there is an affirmation that " At a minimum, the LSP must never be interrupted; this means that the LSP must always have an incoming label and an outgoing label in the LFIB pointing to the correct next-hop label switching router (LSR)" I dont understand, does this affirmation refer to a situation when you have 1 portion of the network which does not know how to reach another portion of the network except of by using an LSP created by MPLS? 2. For example I do have a network that is converged using OSPF and I created some RSVP tunnels (not full mesh of RSVP tunnel as the book suggests, otherwise it would not work) and I had many implicit-null situations, which resulted in traffic being blackholed (this term also confuses me, what is it?) When I enabled LDP over my RSVP tunnels, everything started to work correctly and as far as I understand this happens because of the complete labeling process along the whole path from the source to destination I still do not understand this though, if there is a mandatory condition that every packet should be labeled across the LSP, why the implicit-null stuff exists after all if it causes some packets not being able to reach their destination, and what are the situations/scenarios when a) I can definetly say that my problem is that my traffic is not being tagged across the path and thats why it is being lost b) I can leave some portion of the network with tagging and another without? ****It is a bit difficult for me, because I have never seen a real ISP network, I have a moderate size MAN network, where every customer is visible to one another, so there is no need to hide customers networks. ... View more