44net May 2017

44net@mailman.ampr.org

56 participants
149 discussions

Re: [44net] amprgw routing
by Rob Janssen 02 May '17

02 May '17

> Using a simple global array to be the list of addresses and pointers, > full load time went from about 3ms to 15ms. But it works just fine and > the lookups are so fast the microsecond timer registers zero. Great! I would think that the gain in efficiency of the routing more than offsets the extra processing for setup. You could consider making it multithreaded but I don't think anyone would notice an occasional 15ms delay and/or some drops. On our radio network such behaviour is quite normal. Another possibility would be to first scan for the "common case" of all subnets and gateways remaining the same but only the endpoint address of one or two gateways changing, and in that case omit the entire table setup and only patch the nexthop addresses of those gateways. Rob

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"Sub-routing" from BGP Subnet
by Phil Pacier 02 May '17

02 May '17

Hello all, and thank you for your assistance. I have 44.10.10.0/24 allocated and announced via BGP. The subnet terminates to an Ubuntu server in a data center. I want to allocate addresses from this subnet via tunnels to other locations. For example, I would like to assign an address or a block of addresses to my home location (Cisco 1900 router) from this subnet. Is this possible, or do I need to look at a different option? Thank you! -- 73 de Phil Pacier, AD6NH APRS Tier2 Network Coordinator http://www.aprs2.net

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amprgw routing
by Brian Kantor 01 May '17

01 May '17

I've made some changes to the amprgw routing mechanism. Replacing the earlier sequential search through the routing table with a binary search has significantly sped up lookups, which can happen up to twice per packet forwarded (once for source address, once for destination address). Three times an hour, a background process fetches the encap routing table from the portal, and if it has changed, signals the router process to update its routing table. The routing table update seems to take about 3 msec during which packets can't be looked up and so are not forwarded. This fetch also updates the data source for the rip sender, so you'll receive updates more quickly now. - Brian

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Re: [44net] amprgw routing
by Rob Janssen 01 May '17

01 May '17

> I think the most efficient technique is to make the per-address lookup > table an mmap'd array of pointers to entries in the existing route table. > That makes it effectively addrtable[2][2**24], right? Yes. Of course a single pointer would be 8 bytes when it is compiled for 64 bits, but it would not need to be. When your existing route table is an array rather than a collection of malloc'ed objects linked by pointers, the "pointer" from the address lookup table into the route table could be the smaller index into the route table (that would easily fit in an unsigned short integer, allowing for 65535 gateways). Or, in 32 bit mode a simple pointer can be used (4 bytes per entry). Rob

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Re: [44net] amprgw routing
by Rob Janssen 01 May '17

01 May '17

> You're absolutely right. I dropped some decimal places. Thanks! However, > gateway addresses don't fit in a byte, they're stored in an unsigned long, > which is 4 bytes each. 4 * 16 million, right? And I think you need > counters and flags. So it's an array of structs of some modest size each. My estimate of 128MB was based on having 4 bytes per entry and 2 tables for convenient updating (update one table then toggle a single indicator or pointer to make the updated table active). Of course when you require more bytes per entry the table will expand, but 8-16 bytes per entry should still fit comfortably in a modern machine. > But I see a complication: You will have to have n entries per route, > which will make loading the table a little less straightforward. Well, searching a datastructure for the correct route isn't straightforward either... remember when there is a tunnel to e.g. 44.137.0.0/16 and another one to 44.137.1.80/28 (an example from the current table) then any traffic to 44.137.1.81 should go to the tunnel for 44.137.1.80/28, not something that you can easily do with a binary search. However, a lookup in the table populated with entries for 44.137.0.0/16 and then overwritten with entries for 44.137.1.80/28 is easy. It will find the correct gateway with a single array index operation. So you only need to build the table starting from the subnets sorted by number of subnet bits to get it right. Indeed it is best to make the program multithreaded, or you could put the lookup table in shared memory and have a process doing the routing and another process doing the updating. I would still opt for having a "current" and a "next" table where the routing code always has a working table and the switch to the next version is instaneous. Of course you can also do a quick check before starting the laborious update process, to see if the new encap table is different from the previous one. Rob

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Re: [44net] amprgw routing
by Rob Janssen 01 May '17

01 May '17

> My estimate of 128MB was based on having 4 bytes per entry and 2 tables for > convenient updating (update one table then toggle a single indicator or pointer > to make the updated table active). > Of course when you require more bytes per entry the table will expand, but > 8-16 bytes per entry should still fit comfortably in a modern machine. Another possibility would be to have a 16-million entry array of short integers holding a "gateway number" (starting at 1) for each IP address, and a separate table of gateways holding all the other info you want to keep per gateway. (e.g. counters) Then the processing of a packet would first index the destination IP in the first array, retrieving the gateway number (0 means drop the packet), then use that number as an index in the gateway table to access the per-gateway data including the endpoint address and the counters. This would require only slightly more than 32MB of memory for the tables, which should be no problem without any tricks. Rob

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Re: [44net] amprgw routing
by Rob Janssen 01 May '17

01 May '17

> 128MB is only 3% of 4GB. What would be the problem reserving that for a lookup table? BTW, a nice trick for such tables is to do a mmap of /dev/zero with the proper size as a starting point, then write only the entries that are nonzero. That way the vast spaces that are only zeroes will not occupy physical memory, and when they are read by the forwarding code they read back as zeroes. Linux also has a "|MAP_ANONYMOUS" flag to obtain the same result, I don't know if BSD has that. |Rob

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Re: [44net] amprgw routing
by Rob Janssen 01 May '17

01 May '17

> Interesting concept. Someday if we have enough memory I may try it, but > right now amprgw (an old machine) has only 4 GB of memory. It'd die swapping. 128MB is only 3% of 4GB. What would be the problem reserving that for a lookup table? Rob

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Re: [44net] Shared block lists (was: portal down)
by Tom Hayward 01 May '17

01 May '17

On Sun, Apr 30, 2017 at 5:31 AM, Marc <monsieurmarc(a)btinternet.com> wrote: > Maybe we should start sharing block lists. Marc, HamWAN has a public blacklist system. Feel free to subscribe to it. It does not publish a full list, but rather sends addresses one by one, instantly*, as they are blocked. *It takes about 1.5 seconds for report of a hack attempt to propagate to our logging system, pass analysis, and be published to our edge routers' firewall. Here is the code behind the system (including a Mikrotik script you can use to subscribe): https://github.com/kd7lxl/blacklist-service Anything blocked by the HamWAN network will be published here: http://monitoring.hamwan.net/blacklist If it seems like it's not responding, that's normal. It is an HTTP longpoll service, so it will hang until there is data to be published, then that data is sent immediately. This mechanism allows pushing data (in this case, a blacklisted address) to a Mikrotik router without having to store admin credentials of that router on the blacklist system. Since it uses a standard protocol, it can be adapted for other platforms. Tom KD7LXL

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44net May 2017