Shortly after putting the above-referenced switch in production, I began seeing USL -6 errors in the dashboard's buffered log. Downloading the buffered log as a text file has revealed more information about the errors, thus:
<11> Feb 22 08:46:12 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2142 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 08:46:12 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2143 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 08:46:12 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2144 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 08:46:12 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2145 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 08:46:12 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2146 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 08:46:12 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2147 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 08:53:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2148 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 08:53:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2149 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 08:53:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2150 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 08:53:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2151 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 08:53:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2152 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 08:53:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2153 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<13> Feb 22 08:53:44 10.6.6.253-1 TRAPMGR[42135668]: traputil.c(701) 2154 %% Link Down: 31
<11> Feb 22 09:07:14 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2155 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 09:07:14 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2156 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 09:07:14 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2157 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 09:07:14 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2158 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 09:07:14 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2159 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 09:07:14 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2160 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 09:07:20 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2161 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 09:07:20 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2162 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 09:07:20 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2163 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 09:07:20 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2164 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 09:07:20 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2165 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 09:07:20 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2166 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 09:23:57 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2169 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 09:23:57 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2170 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 09:23:57 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2171 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 09:23:57 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2172 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 09:23:57 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2173 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 09:23:57 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2174 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 09:28:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2175 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 09:28:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2176 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 09:28:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2177 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 09:28:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2178 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 09:28:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2179 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 09:28:11 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2180 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 09:28:11 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2181 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 09:28:11 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2182 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 09:28:11 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2183 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 09:28:11 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2184 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 09:28:11 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2185 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 09:28:17 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2186 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 09:28:17 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2187 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 09:28:17 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2188 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 09:28:17 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2189 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 09:28:17 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2190 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 09:28:17 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2191 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 11:37:46 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2195 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 11:37:46 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2196 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 11:37:46 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2197 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 11:37:46 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2198 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 11:37:46 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2199 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 11:37:51 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2200 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 11:37:51 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2201 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 11:37:51 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2202 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 11:37:51 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2203 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 11:37:51 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2204 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 11:37:51 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2205 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 11:56:33 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2206 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 11:56:33 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2207 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 11:56:33 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2208 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 11:56:33 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2209 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 11:56:33 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2210 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 11:56:33 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2211 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 11:59:58 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2212 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 11:59:58 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2213 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 11:59:58 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2214 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 11:59:58 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2215 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 11:59:58 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2216 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 11:59:58 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2217 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<13> Feb 22 12:00:01 10.6.6.253-1 TRAPMGR[42135668]: traputil.c(701) 2218 %% Link Down: 9
<13> Feb 22 12:00:04 10.6.6.253-1 TRAPMGR[42135668]: traputil.c(701) 2219 %% Link Up: 9
<13> Feb 22 12:00:10 10.6.6.253-1 TRAPMGR[42135668]: traputil.c(701) 2220 %% Link Down: 9
<13> Feb 22 12:00:14 10.6.6.253-1 TRAPMGR[42135668]: traputil.c(701) 2221 %% Link Up: 9
<11> Feb 22 12:00:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2222 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 12:00:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2223 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 12:00:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2224 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 12:00:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2225 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 12:00:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2226 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 12:00:44 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2227 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 12:09:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2228 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 12:09:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2229 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 12:09:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2230 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 12:09:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2231 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 12:09:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2232 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 12:09:10 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2233 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 12:19:27 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2234 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 12:19:27 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2235 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 12:19:27 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2236 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 12:19:27 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2237 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 12:19:27 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2238 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 12:19:27 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2239 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<11> Feb 22 12:25:53 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2240 %% USL returned -6 while adding 01:00:5e:00:00:fa vid 1.
<11> Feb 22 12:25:53 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2241 %% USL returned -6 while adding 01:00:5e:00:01:3c vid 1.
<11> Feb 22 12:25:53 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2242 %% USL returned -6 while adding 01:00:5e:59:bc:01 vid 1.
<11> Feb 22 12:25:53 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2243 %% USL returned -6 while adding 01:00:5e:7f:03:16 vid 1.
<11> Feb 22 12:25:53 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2244 %% USL returned -6 while adding 01:00:5e:7f:ff:fa vid 1.
<11> Feb 22 12:25:53 10.6.6.253-1 DRIVER[42220892]: broad_l2_mcast.c(1804) 2245 %% USL returned -6 while adding 01:00:5e:7f:ff:fb vid 1.
<14> Feb 22 12:34:43 10.6.6.253-1 USER_MGR[42121252]: user_mgr_util.c(1588) 2246 %% HTTP Session 35 started for user admin connected from 10.6.6.4
Obviously something is not right with some multicast capability of the switch, but I'm curious as to what the exact problem might be (and how to fix or work around it). This problem has persisted through versions 2.10, 2.11, 2.12, and 2.13 of the switch's firmware, and seems to be getting worse with time. I had noticed an uptick in multicast traffic on the network after introducing the switch, and the amount of that traffic (much of which may be spurious) also seems to be increasing with time.
Any help with, or insight into, this issue would be greatly appreciated.